Guido Ferretti

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Jean-Christophe Plantin

London School of Economics and Political Science

David Seamon

Kansas State University

Wei-chieh Tsai

National Chung Cheng University

Theodore Arabatzis

National & Kapodistrian University of Athens

Giulia Sissa

Ucla

Gustavo Caponi

Universidade Federal de Santa Catarina - UFSC (Federal University of Santa Catarina)

Viacheslav Kuleshov

Stockholm University

Linda Rui Feng

University of Toronto

José Manuel Santos

University of Salamanca

Mario Cams 康言

KU Leuven

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Papers by Guido Ferretti

Energetics of Muscular Exercise

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A century of exercise physiology: key concepts on coupling respiratory oxygen flow to muscle energy demand during exercise

European Journal of Applied Physiology, 2022

After a short historical account, and a discussion of Hill and Meyerhof’s theory of the energetic... more After a short historical account, and a discussion of Hill and Meyerhof’s theory of the energetics of muscular exercise, we analyse steady-state rest and exercise as the condition wherein coupling of respiration to metabolism is most perfect. The quantitative relationships show that the homeostatic equilibrium, centred around arterial pH of 7.4 and arterial carbon dioxide partial pressure of 40 mmHg, is attained when the ratio of alveolar ventilation to carbon dioxide flow ($${\dot{V}}_{A}/{\dot{V}}_{R}{CO}_{2}$$ V ˙ A / V ˙ R CO 2 ) is − 21.6. Several combinations, exploited during exercise, of pertinent respiratory variables are compatible with this equilibrium, allowing adjustment of oxygen flow to oxygen demand without its alteration. During exercise transients, the balance is broken, but the coupling of respiration to metabolism is preserved when, as during moderate exercise, the respiratory system responds faster than the metabolic pathways. At higher exercise intensities, ear...

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The role of pulmonary CO2 flow in the control of the phase I ventilatory response to exercise in humans

The effects of b1-adrenergic blockade on cardiovascular oxygen flow in normoxic and hypoxic humans at exercise

Eur J Appl Physiol, 2005

Can 99mTcO4- (Tc) replace 131I (I) for pre-ablation scintigraphy after thyroidectomy (TRD) for differentiated thyroid cancer? Our experience in 508 pts

Society of Nuclear Medicine Annual Meeting Abstracts, May 1, 2012

424 Objectives To examine if Tc is adeguate for post TRD scan and verify if the lower radiation d... more 424 Objectives To examine if Tc is adeguate for post TRD scan and verify if the lower radiation dose delivered to remnant thyroid tissue, reducing stunning can improve outcome after ablative I therapy. Methods 508 consecutive pts after TRD for non metastatic papillary or follicular cancer of the thyroid (TSH>30mIU/mL) entered the study and were divided into 2 groups (G): G1 (176 pts, from 2002 to 2004) had a scan with 185 MBq of I; G2 (318 pts, from 2005 to 2009) had a scan with 370 MBq of Tc. 14/508 pts had a Tc not detecting tissue remnant and were excluded. In case of scan evidence of residual thyroid tissue, after 72h from diagnostic dose of Tc or I, pts of both groups were treated with a standard dose of 3.7 GBq of I to ablate the remnant thyroid tissue. We considered the ablation was successfully if at 1 year a negative thyroid scan and an undetectable serum thyroglobulin (Tg) level ( 0.05 were considered of statistical consistency. Results The 2 G were comparable (Tab) as for age, sex ratio, tumour type, stage, Tg and AbTg (p > 0.05). Only 14/318 Tc scans did not detect remnant tissue, while among them in 7/14 pts a subsequent I scan did detect it. Based on 1y negative scan-Tg-AbTg successful ablation were obtained in 111/176 (63%) in G1 and in 270/318 (85%) in G2 and in 116/176 (66%) in G1 and 290/318 (91%) in G2, if just a negative scan was considered as successful ablation (Tab) (p Conclusions Tc could be the first choice for post TRD scan, reserving I only in case of a negative scan. The better post ablation outcome which follows Tc scintigraphy is suggestive of some thyroid radiation stunning after I scintigraphy and this should further push to replace I with Tc for post TRD scan

Cardiovascular responses to dry resting apnoeas in elite divers while breathing pure oxygen

Respiratory Physiology & Neurobiology, 2015

We hypothesized that the third dynamic phase (3) of the cardiovascular response to apnoea require... more We hypothesized that the third dynamic phase (3) of the cardiovascular response to apnoea requires attainment of the physiological breaking point, so that the duration of the second steady phase (2) of the classical cardiovascular response to apnoea, though appearing in both air and oxygen, is longer in oxygen. Methods: Nineteen divers performed maximal apnoeas in air and oxygen. We measured beat-by-beat arterial pressure, heart rate (f H), stroke volume (SV), cardiac output (Q). Results: The f H , SV andQ changes during apnoea followed the same patterns in oxygen as in air. Duration of steady 2 was 105 ± 37 and 185 ± 36 s, in air and oxygen (p < 0.05), respectively. At end of apnoea, arterial oxygen saturation was 1.00 ± 0.00 in oxygen and 0.75 ± 0.10 in air. Conclusions: The results support the tested hypothesis. Lack of hypoxaemia during oxygen apnoeas suggests that, if chemoreflexes determine 3, the increase in CO 2 stores might play a central role in eliciting their activation.

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Maximal instantaneous muscular power after prolonged bed rest in humans

Journal of applied physiology (Bethesda, Md. : 1985), 2001

A reduction in lower limb cross-sectional area (CSA) occurs after bed rest (BR). This should lead... more A reduction in lower limb cross-sectional area (CSA) occurs after bed rest (BR). This should lead to an equivalent reduction in maximal instantaneous muscular power (W(p)) if the body segments' lengths remain unchanged. W(p) was determined during maximal jumps off both feet on a force platform before and on days 2, 6, 10, 32, and 48 after a 42-day duration BR. CSA of thigh muscles was measured by magnetic resonance imaging before and on day 5 after BR. Before BR, W(p) was 3.63 +/- 0.43 kW or 48.6 +/- 3.3 W/kg. On days 2 and 6 after BR, W(p) was reduced by 23.7 +/- 6.9 and 22.7 +/- 5.4% (P < 0.01), respectively. Thigh extensors CSA (CSAEXT) was 16.7 +/- 4.7% (P < 0.01) lower than before. When normalized per CSAEXT, W(p) was reduced by only 4.8 +/- 4.5% (P < 0.05). By day 48 of recovery, W(p) had returned to baseline values. Therefore, if W(p) is appropriately normalized for CSA of the extensor muscles, the reduction in CSAEXT explains most of the decrease in W(p) decreas...

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Lactate and epinephrine during exercise in altitude natives

Journal of applied physiology (Bethesda, Md. : 1985), 1996

We tested the hypothesis that the reported low blood lactate accumulation ([La]) during exercise ... more We tested the hypothesis that the reported low blood lactate accumulation ([La]) during exercise in altitude-native humans is refractory to hypoxianormoxia transitions by investigating whether acute changes in inspired O2 fraction (FIo2) affect the [La] vs. power output (W) relationship or, alternatively, as reported for lowlanders, whether changes in [La] vs. W on changes in FIo2 are related to changes in blood epinephrine concentration ([Epi]). Altitude natives [n = 8, age 24 +/- 1 (SE) yr, body mass 62 +/- 3 kg, height 167 +/- 2 cm] in La Paz, Bolivia (3,600 m) performed incremental exercise with two legs and one leg in chronic hypoxia and acute normoxia (AN). Submaximal one- and two-leg O2 uptake (Vo2) vs. W relationships were not altered by FIo2. AN increased two-leg peak Vo2 by 10% and peak W by 7%. AN paradoxically decreased one-leg peak Vo2 by 7%, whereas peak W remained the same. The [La] vs. W relationships were similar to those reported in unacclimatized lowlanders. There...

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Muscle tissue adaptations of high-altitude natives to training in chronic hypoxia or acute normoxia

Journal of applied physiology (Bethesda, Md. : 1985), 1996

Twenty healthy high-altitude natives, residents of La Paz, Bolivia (3,600 m), participated in 6 w... more Twenty healthy high-altitude natives, residents of La Paz, Bolivia (3,600 m), participated in 6 wk of endurance exercise training on bicycle ergometers, 5 times/wk, 30 min/session, as previously described in normoxia-trained sea-level natives (H. Hoppeler, H. Howald, K. E. Conley, S. L. Lindstedt, H. Claassen, P. Vock, and E. R. Weibel. J. Appl. Physiol. 59: 320-327, 1985). A first group of 10 subjects was trained in chronic hypoxia (HT; barometric pressure = 500 mmHg; inspired O2 fraction = 0.209); a second group of 10 subjects was trained in acute normoxia (NT; barometric pressure = 500 mmHg; inspired O2 fraction = 0.314). The workloads were adjusted to approximately 70% of peak O2 consumption (VO2peak) measured either in hypoxia for the HT group or in normoxia for the NT group. VO2peak determination and biopsies of the vastus lateralis muscle were taken before and after the training program. VO2peak in the HT group was increased (14%) in a way similar to that in NT sea-level nati...

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Ventilatory response at the onset of exercise: an update of the neurohumoral theory

Advances in experimental medicine and biology, 1993

There appears to be agreement on the fact that the ventilatory response at the onset of a constan... more There appears to be agreement on the fact that the ventilatory response at the onset of a constant-load exercise is characterized in man by two components (Dejours, 1963): a) an abrupt reflex response (“phase I”, ph 1 ventilatory response, according to the definition of Wasserman, 1978), most probably originating from the contracting muscles, whose afferent pathway is presumably represented by the group III spinal afferent fibers (Mitchell et al., 1977; Mitchell, 1990); b) a delayed response (“phase II and III”, ph2 and ph3), mainly controlled by the endogenous production of CO2. The way these components interact has been for a long time, and still is, a matter for discussion.

Training in hypoxia vs. training in normoxia in high-altitude natives

Journal of applied physiology (Bethesda, Md. : 1985), 1995

To determine the interactions between endurance training and hypoxia on maximal exercise performa... more To determine the interactions between endurance training and hypoxia on maximal exercise performance, we performed a study on sedentary high-altitude natives who were trained in normoxia at the same relative (n = 10) or at the same absolute (n = 10) intensity of work as hypoxia-trained subjects (n = 10). The training-induced improvement of maximal oxygen uptake (VO2max) in hypoxia-trained subjects was similar to that obtained in normoxia-trained sea-level natives submitted to the same training protocol (H. Hoppeler, H. Howald, K. Conley, S. L. Lindstedt, H. Claassen, P. Vock, and E. W. Weibel. J. Appl. Physiol. 59: 320-327, 1985). Training at the same absolute work intensity in the presence of increased oxygen delivery failed to provide a further increase in VO2max. VO2max was not improved to a greater extent by simultaneously increasing absolute work intensity and O2 delivery during the training sessions. In addition, training in normoxia is accompanied by an increased blood lactat...

Maximal exercise performance in chronic hypoxia and acute normoxia in high-altitude natives

Journal of applied physiology (Bethesda, Md. : 1985), 1995

Maximal O2 uptake (VO2max) was determined on a bicycle ergometer in chronic hypoxia (CH) and duri... more Maximal O2 uptake (VO2max) was determined on a bicycle ergometer in chronic hypoxia (CH) and during acute exposure to normoxia (AN) in 50 healthy young men who were born and had lived at 3,600 m altitude (La Paz, Bolivia). VO2max was significantly improved (approximately 8%) by AN. However, the difference in VO2max measured in CH and AN (delta VO2max) was lower than that reported in sea-level natives (SN) who exercised in chronic normoxia and acute hypoxia. It is shown that high-altitude natives (HN) and SN have a similar VO2max in normoxia, but highlanders can attain a greater VO2max when O2 availability is reduced by altitude exposure. In addition, in HN, the higher the subject's VO2max in hypoxia, the smaller his delta VO2max. These results contrast with the data obtained in 14 lowlanders acclimatized to high altitude who showed that their delta VO2max was positively related to their VO2max in hypoxia, as previously reported in SN who exercised in acute hypoxia (A. J. Young, ...

Effects of exercise on maximal instantaneous muscular power of humans

Journal of applied physiology (Bethesda, Md. : 1985), 1987

The maximal instantaneous anaerobic power (w), as determined during a high jump off both feet on ... more The maximal instantaneous anaerobic power (w), as determined during a high jump off both feet on a force platform, was measured on eight subjects starting from a resting base line; a base line of steady-state cycloergometric exercise requiring 30, 50, and 70% of individual maximum O2 consumption (VO2max); and a base line of maximal and supramaximal exercise (100 and 120% of VO2max). In addition, w was also measured during the VO2 transients from rest to each of the above work loads. Blood lactate concentration ([Lab]) was determined before and 8 min after the end of each priming load. After the onset of any priming load, w decreases with time reaching in 2 min a steady level that is lower the higher the VO2. For the three lowest work rates, the steady w level is unchanged by increasing the duration of the priming exercise up to 30 min. For low work levels, the decrease of w as a function of VO2 is essentially parallel to that of estimated muscle concentration of ATP ([ATP]). For wor...

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Regulation of perfusive O2 transport during exercise in humans: effects of changes in haemoglobin concentration

The Journal of physiology, 1992

1. Recently it was suggested that submaximal cardiac output (Q) could vary in response to changes... more 1. Recently it was suggested that submaximal cardiac output (Q) could vary in response to changes in arterial O2 concentration (Ca,O2), so that arterial O2 delivery (Qa,O2 = Q x Ca,O2, in ml min-1) is kept constant. 2. This hypothesis was tested on eight healthy male subjects, at rest and during exercise (50, 100 and 150 W) in three conditions: normaemia (N), after 6 weeks of endurance training (T), and 2 days after subsequent autologous blood reinfusion (P). 3. Measured variables were oxygen consumption (VO2), by open circuit method, Q, by a CO2 rebreathing method, and haemoglobin concentration ([Hb]), by a photometric method. Ca,O2 was calculated as the product of [Hb], arterial O2 saturation (0.97), and the O2 binding coefficient. 4. [Hb] and thus Ca,O2 increased by 2.6% (T vs. N) and subsequently by further 5.8% (P vs. T). VO2 and Qa,O2 were linear functions of power (w), both relationships being unaffected by changes in Ca,O2. As a consequence, the linear Q vs. VO2 relationship...

The decrease of maximal oxygen consumption during hypoxia in man: a mirror image of the oxygen equilibrium curve

The Journal of Physiology, 1997

1. Endurance athletes (E) undergo a marked reduction of arterial 02 saturation (Sa02) at maximal ... more 1. Endurance athletes (E) undergo a marked reduction of arterial 02 saturation (Sa02) at maximal exercise in normoxia, which disappears when they breathe hyperoxic mixtures. In addition, at a given level of hypoxia, the drop in maximal 02 consumption (T42max) is positively related to the individual normoxic V02,max. 2. These data suggest that the curve relating V02,max to P1I02 may be steeper and perhaps less curved in E than in sedentary subjects (S) with low Vo2 max values because of the greater hypoxaemia in the latter, whence the hypotheses that (i) the relationship between V02 max and PI,02 may be set by the shape of the oxygen equilibrium curve; and (ii) the differences between E and S may be due to the different position on the oxygen equilibrium curve on which these subjects operate. These hypotheses have been tested by performing a systematic comparison of the Vo2 max or 5a,02 VS. PI02 relationships in E and S. 3. On ten subjects (five S and five E), V02 max was measured by standard procedure during cycloergometric exercise. Sa°2 was measured by fingertip infrared oximetry. Arterialized blood P02 (Pa,o2) and Pco2 (Pa,co2) were determined in 80 #1 blood samples from an ear lobe. The subjects breathed ambient air or a N2-02 mixture with an inspired 02 fraction (FIj 02) of 0 30, 0-18, 016, 013 and 0 11, respectively. V2,max was normalized with respect to that obtained at the highest F 02. 4. The relationships between Sao02 or normalized I 2,max and FI A (or PL02) had similar shapes, the data for E being systematically below and significantly different from those for S. Linear relationships between 2ao°and normalized '42,max, statistically equal between E and S, were found. 5. We conclude that the relationships between either V02,max or Sa.O2 and FI A (or Pa,o2) may indeed be the mirror images of one another, implying a strict link between the decrease of V2,max in hypoxia and the shape of the oxygen equilibrium curve, as hypothesized. The classical non-linear relationship between maximal oxygen consumption (V0, max) and inspired oxygen partial pressure (PI 2) in hypoxia (

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The diagram: An analytical interpretation of oxygen transport in arterial blood during exercise in humans

Respiratory Physiology & Neurobiology, 2014

A new analysis of the relationship between cardiac output (Q˙) and oxygen consumption V˙O2 is pre... more A new analysis of the relationship between cardiac output (Q˙) and oxygen consumption V˙O2 is presented (Q˙-V˙O2 diagram). Data from different sources in the literature have been used for validation in three conditions: exercise and rest in normoxia, and exercise in hypoxia. The effects of changes in arterial oxygen concentration CaO2 on Q˙ are discussed, as well as the effects of predominant sympathetic or vagal stimulation. Differences appear depending on whether CaO2 is varied by means of changes in blood haemoglobin concentration or changes in arterial oxygen saturation. The present Q˙-V˙O2 diagram allows comprehensive description of oxygen transport in exercising humans; it expands applicability of the historical Q˙-V˙O2 relationship to include CaO2 variations; it opens new pathways for understanding underlying mechanisms; it allows computation of Q˙ from CaO2 and V˙O2 measurements, when Q˙ cannot be measured.

Energy cost of walking and running at extreme uphill and downhill slopes

Journal of Applied Physiology, 2002

The costs of walking (Cw) and running (Cr) were measured on 10 runners on a treadmill inclined be... more The costs of walking (Cw) and running (Cr) were measured on 10 runners on a treadmill inclined between −0.45 to +0.45 at different speeds. The minimum Cw was 1.64 ± 0.50 J · kg−1 · m−1 at a 1.0 ± 0.3 m/s speed on the level. It increased on positive slopes, attained 17.33 ± 1.11 J · kg−1 · m−1 at +0.45, and was reduced to 0.81 ± 0.37 J · kg−1 · m−1 at −0.10. At steeper slopes, it increased to reach 3.46 ± 0.95 J · kg−1 · m−1 at −0.45. Cr was 3.40 ± 0.24 J · kg−1 · m−1 on the level, independent of speed. It increased on positive slopes, attained 18.93 ± 1.74 J · kg−1 · m−1 at +0.45, and was reduced to 1.73 ± 0.36 J · kg−1 · m−1 at −0.20. At steeper slopes, it increased to reach 3.92 ± 0.81 J · kg−1 · m−1 at −0.45. The mechanical efficiencies of walking and running above +0.15 and below −0.15 attained those of concentric and eccentric muscular contraction, respectively. The optimum gradients for mountain paths approximated 0.20–0.30 for both gaits. Downhill, Cr was some 40% lower than ...

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A beat-by-beat analysis of cardiovascular responses to dry resting and exercise apnoeas in elite divers

by Renza Perini, Guido Ferretti, and Andrea Sivieri

European Journal of Applied Physiology, 2014

Cardiovascular responses during resting apnoea include three phases: (1) a dynamic phase of rapid... more Cardiovascular responses during resting apnoea include three phases: (1) a dynamic phase of rapid changes, lasting at most 30 s; (2) a subsequent steady phase; and (3) a further dynamic phase, with a continuous decrease in heart rate (HR) and an increase in blood pressure. The interpretation was that the end of the steady phase corresponds to the physiological apnoea breaking point. This being so, during exercise apnoeas, the steady phase would be shorter, and the rate of cardiovascular changes in the subsequent unsteady phase would be faster than at rest. To test these hypotheses, we measured beat-by-beat systolic (SBP), diastolic, and mean blood pressures (MBP), HR, and stroke volume (SV) in six divers during dry resting (duration 239.4 ± 51.6 s) and exercise (30 W on cycle ergometer, duration 88.2 ± 20.9 s) maximal apnoeas, and we computed cardiac output ([Formula: see text]) and total peripheral resistance (TPR). Compared to control, at the beginning of resting (R1) and exercising (E1) apnoeas, SBP and MBP decreased and HR increased. SV and [Formula: see text] fell, so that TPR remained unchanged. At rest, HR, SV, [Formula: see text], and SBP were stable during the subsequent phase; this steady phase was missing in exercise apnoeas. Subsequently, at rest (R3) and at exercise (E2), HR decreased and SBP increased continuously. SV returned to control values. Since [Formula: see text] remained unchanged, TPR grew. The lack of steady phase during exercise apnoeas suggests that the conditions determining R3 were already attained at the end of E1. This being so, E2 would correspond to R3.