Ventilatory response to CO2 at rest and during positive and negative work in normoxia and hyperoxia

Summary Ventilation versus alveolar relationships were determined by the steady-state method in 6 normal male subjects at rest and during positive and negative work at one load in both normoxic and hyperoxic condition. In 5 subjects the slopes of the lines during positive and negative work increased in normoxia as compared with rest. This effect was less evident in hyperoxia. It was also found that the slopes of the lines in positive and in negative work were about the same in both normoxic and hyperoxic conditions. Oxygen uptake and CO₂ production during positive work is higher than during negative work.These results suggest that: 1) the disagreement between various authors on the change of the slope of the line may be due to the differences in the method of calculation of the slope or the method of the determination of lines; 2) the stimuli from the muscle spindles in the working muscle during exercise probably do not contribute to the increase in ventilatory response to CO₂; 3) the increased slope of the normoxic line during exercise may be due to the interaction of several factors such as impulses from working muscles, chemosensitivity of central or peripheral chemoreceptors, adrenal-sympathetic pathways or temperature; 4) respiratory oscillations of or do not seem to influence the respiratory response to CO₂.This study was supported in part by a grant from the Netherlands Organization for the Advancement of Pure Research (Z.W.O.)     

Reliability of the cardiac output measurement with the indirect Fick-principle for CO2 during exercise

Cardiac output measurements were performed during 50 exercise tests in 16 normal subjects employing the indirect Fick principle for CO₂. During sub-maximal steady state exercise the plateau CO₂ tension ( ) was estimated with a rebreathing procedure. The mixed venous CO₂ tension ( ) was calculated by subtracting the alveolocapillary CO₂ tension difference from the . Compared with data from the literature the most valid calculation of the cardiac output was obtained by using the . Cardiac output values, calculated via the turned out to be too low.The reproducibility was tested by repitition of 18 exercise tests at least after 5 days. The relative standard error of a single observation was 4.1% for the cardiac output, which was found to be as good as that of invasive measurements.     

Einstellzeit der Pt-Elektrode bei Messungen nicht stationärer O2-Partialdrucke

Zusammenfassung Das Meßsignal bei sprunghaftenpO₂-Änderungen wird anhand des Diffusionsfeldes der Elektrode beschrieben. Es wird das zeitliche Verhalten des Meßsignals von blanken und membranbespannten Elektroden in gasförmigen und nicht gasförmigen Meßmedien betrachtet. Aus dem Verhalten des Meßsignals kann jeweils die Einstellzeit alssystematischer Meßfehler abgeleitet werden. In nicht gasförmigen Medien (z. B. biologisches Gewebe) übersteigt das Meßsignal nach einempO₂-Sprung zu höheren Werten das stationäre Endsignal. Daraus ergibt sich eine besondere Betrachtung der Einstellzeit in solchen Medien.Die Einstellzeit für Pt-Elektroden mit einfacher und doppelter Membran wird explizit angegeben. Schließlich wird für biologische Medien die Einstellzeit mit dem Diffusionsfehler [8] verglichen. Die Forderungen an eine Membran der Pt-Elektrode mit kleiner Einstellzeit und gleichzeitig kleinem Diffusionsfehler sind zusammengestellt.

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Erklärung der Symbole a Verhältnis der Diffusionskoeffizienten zweier Membranen - Bunsenscher Löslichkeitskoeffizient des Mediums - _m Bunsenscher Löslichkeitskoeffizient der Membran - b Verhältnis der Diffusionsleitfähigkeiten von Membran und Medium - C ₁,C ₂ Proportionalitätskonstanten zwischen Meßsignal und O₂-Partialdruck - D Diffusionskoeffizient des Mediums - D _m,D _m Diffusionskoeffizienten der Membranen - Diffusionskoeffizient der effektiven Membran - DF Diffusionsfehler - DGl Differentialgleichung - d _m,d _m Dicke der Membranen - Dicke der effektiven Membran - dimensionsloser Parameter des Diffusionsfehlers - erf Fehlerfunktion - exp Exponentialfunktion - F Faradaykonstante - grad Gradient - I stationäres Meßsignal vor dempO₂-Sprung - I stationäres Meßsignal nach dempO₂-Sprung - I(t), I(),I() instationäres Meßsignal als Funktion der Zeit bzw. zeitabhängiger dimensionsloser Parameter - K Diffusionsleitfähigkeit des Mediums - K _m Diffusionsleitfähigkeit der Membran - Diffusionsleitfähigkeit der effektiven Membran - dimensionsloser Parameter - n Summationsindex - pO₂ O₂-Partialdruck - pO₂ als Funktion von Ort und Zeit bzw. zeitabhängiger dimensionsloser Parameter; Diffusionsfeld der Elektrode - p _c konstanterpO₂ vor dempO₂-Sprung - p _c konstanterpO₂ nach dempO₂-Sprung - p(r ₀+d _m , ) pO₂ an der Grenze Membran/Medium in Abhängigkeit des Zeitparameters - p(r,o) Diffusionsfeld zum Zeitpunkt (t=0) despO₂-Sprunges - p(r₀+d_m, o) pO₂ an der Grenze Membran/Medium zum Zeitpunkt despO₂-Sprunges - R Radius der ebenen, kreisförmigen Elektrode - r ₀ Radius der Elektrode mit halbkugelförmiger Pt-Oberfläche - r Kugelkoordinate - ₁,₂ dimensionslose ortsabhängige Parameter - T ₉₀,T ₉₅ Zeit, bis 90% bzw. 95% des Signalunterschiedes nach dempO₂-Sprung ausgeglichen sind (Einstellzeit) - T ₉₀,T ₉₅ Einstellzeit der Elektrode mit Doppelmembran - T _90*,T _95* Zeit, bis sich das Signal nach Übersteigen des stationären Endwertes diesem auf 10% bzw. 5% angenähert hat - dimensionslose Parameter zu den vorangegangenen Einstellzeiten - t Zeitkoordinate - , dimensionslose zeitabhängige Parameter - t _max, _max Zeit maximaler Signalhöhe nachpO₂-Sprung und zugehöriger dimensionsloser Parameter - V(t) Diffusionsgesamtfluß zur Pt-Oberfläche - Stromdichtevektor der diffundierenden O₂-Moleküle - x, y, z Kartesische Koordinaten - Integrationsvariable - ² Laplace-Operator - partielle Ableitung nach der Zeit - Integral über eine Fläche - gerichtetes Flächenelement     

Alveolar oxygen tension in anesthetized,artificially ventilated dogs

Summary Moment-to-moment variation of effective alveolar ( ) during the respiratory cycle was calculated based on a two-alveolar lung model in dogs anesthetized and pump-ventilated under various conditions induced by continuous infusion of sympathomimetics. Under fixed ventilation the amplitude of respiratory fluctuation of ( ) increased with while did not show any correlation withV _D/V _T or with the fraction of effective alveoli. Ideal alveolar in the same situation was near the peak of fluctuating , thus higher than mean effective alveolar by about 4 to 5 mm Hg. This difference of and might be attributed to the difference in respiratory pattern, i.e., constant one-way flow as against periodic ventilation.     

CO2-ventilatory response of the anesthetized rat by rebreathing technique

The ventilatory response to CO₂ in rats under sodium pentobarbital anesthesia has been measured using the rebreathing technique. The animal rebreathed through a tracheal cannula for a period of 4 min from an apparatus of 200–400 ml capacity, containing 5–6% CO₂ in O₂. in the rebreathing apparatus (PappCO₂), instantaneousV _T,f, and were monitored before, during, and after rebreathing. During the rebreathing run,PappCO₂ andPa _CO2 rose linearly from 35–40 to 65–70 mm Hg; there was no significant difference betweenPappCO₂ andPa _CO2 at any time during rebeathing.V _T and increased almost linearly with the rise inPappCO₂, whilef increased to a maximum within 2 min of rebreathing. In the rat,V _T regulation seemed to operate exclusively as a proportional control system in response to linearly increasing CO₂ stimulus. The slopes ofPappCO₂,V _T or response curves varied considerably during the time course of the experiment, depending upon the level of anesthesia, even though there was no large change in in the control periods which were under hyperoxic conditions. However, a significant linear relationship was seen betweenf in the respective control period and the slope ofPappCO₂-V _T response at various levels of anesthesia. We concluded that the rebreathing technique can be applied in small experimental animals and that changes in the sensitivity of the respiratory control system to a CO₂ stimulus by anesthesia can be easily monitored by repeating the rebreathing test.     

A method for estimating bicarbonate buffering of lactic acid during constant work rate exercise

A method to estimate the CO₂ derived from buffering lactic acid by HCO₃ ^– during constant work rate exercise is described. It utilizes the simultaneous continuous measurement of O₂ uptake ( O₂) and CO₂ output ( CO₂), and the muscle respiratory quotient (RQ_m). The CO₂ generated from aerobic metabolism of the contracting skeletal muscles was estimated from the product of the exercise-induced increase in O₂ and RQ_m calculated from gas exchange. By starting exercise from unloaded cycling, the increase in CO₂ stores, not accompanied by a simultaneous decrease in O₂ stores, was minimized. The total CO₂ and aerobic CO₂ outputs and, by difference, the millimoles (mmol) of lactate buffered by HCO₃ ^– (corrected for hyperventilation) were estimated. To test this method, ten normal subjects performed cycling exercise at each of two work rates for 6 min, one below the lactic acidosis threshold (LAT) (50 W for all subjects), and the other above the LAT, midway between LAT and peak O₂ [mean (SD), 144 (48) W]. Hyperventilation had a small effect on the calculation of mmol lactate buffered by HCO₃ ^– [6.5 (2.3)% at 6 min in four subjects who hyperventilated]. The mmol of buffer CO₂ at 6 min of exercise was highly correlated (r = 0.925, P < 0.001) with the increase in venous blood lactate sampled 2 min into recovery (coefficient of variation = ±0.9 mmol·l^–1). The reproducibility between tests done on different days was good. We conclude that the rate of release of CO₂2 from HCO₃ ^– can be estimated from the continuous analysis of simultaneously measured CO₂, O₂, and an estimate of muscle substrate.     

Effects of temperature on the maximal instantaneous muscle power of humans

Summary The maximal instantaneous muscle power ( ) probably reflects the maximal rate of adenosine 5-triphosphate (ATP) hydrolysis ( ), a temperature-dependent variable, which gives rise to the hypothesis that temperature, by affecting , may also influence . This hypothesis was tested on six subjects, whose vastus lateralis muscle temperature (T _muscle) was monitored by a thermocouple inserted approximately 3 cm below the skin surface. The was determined during a series of high jumps off both feet on a force platform before and after immersion up to the abdomen for 90 min in a temperature controlled (T=20±0.1°C) water bath. ControlT _muscle was 35.8±0.7°C, with control being 51.6 (SD 8.7) W · kg^–1. After cold exposure,T _muscle decreased by about 8°C, whereas 27% lower. The temperature dependence of was found to be less (Q ₁₀ < 1.5, whereQ ₁₀ is the temperature coefficient as calculated in other studies) than reported in the literature for . Such a lowQ ₁₀ may reflect an increase in the mechanical equivalent of ATP splitting, as a consequence of the reduced velocity of muscle contraction occurring at lowT _muscle.     

Ventilatory response of prepubertal boys and adults to carbon dioxide at rest and during exercise

Summary The aim of this study was to determine whether the greater ventilation in children at rest and during exercise is related to a greater CO₂ ventilatory response. The CO₂ ventilatory response was measured in nine prepubertal boys [10.3 years (SD 0.1)] and in 10 adults [24.9 years (SD 0.8)] at rest and during moderate exercise ( CO₂ = 20 ml·kg^–1·min^–1) using the CO₂-rebreathing method. Three criteria were measured in all subjects to assess the ventilatory response to CO₂: the CO₂ sensitivity threshold (Th), which was defined as the value of end titalPCO₂ (P _ETCO₂) where the ventilation increased above its steady-state level; the reactivity slope expressed per unit of body mass (SBM), which was the slope of the linear relation between minute ventilation ( _E) andP _ETCO₂ above Th; and the slope of the relationship between the quotient of tidal volume (V _T) and inspiration time (t _I) andP _ETCO₂ (V _T ·t _I ^–1 ·P _ETCO₂ ^–1) values above Th. The _E,V _T, breathing frequency (f _R), oxygen uptake ( O₂), and CO₂ production ( CO₂) were also measured before the CO₂-rebreathing test. The following results were obtained. First, children had greater ventilation per unit body weight than adults at rest (P<0.001) and during exercise (P<0.01). Second, at rest, onlyV _T ·t _I ^–1 ·P _ETCO₂ ^–1 was greater in children than in adults (P<0.001). Third, during exercise, children had a higher S_BM (P < 0.02) andV _T ·t _I ^–1 ·P _ETCO₂ ^–1 (P<0.001) while Th was lower (P<0.02). Finally, no correlation was found between _E/ CO₂ and Th while a significant correlation existed between _E/ CO₂ and S_BM (adults,r=0.79,P<0.01; children,r=0.73,P<0.05). We conclude that children have, mainly during exercise, a greater sensitivity of the respiratory centres than adult. This greater CO₂ sensitivity could partly explain their higher ventilation during exercise, though greater CO₂ production probably plays a role at rest.     

Fast measurement of the CO2 partial pressure in gases and fluids

A CO₂-electrode system consisting of a membrane covered pH electrode, an electronic antilog modul and a special electronic analog circuit is described. Since the electrode output signal is a logarithmic function of the CO₂ partial pressure the output signal of the antilog module is proportional to the CO₂ partial pressure. The time course of the electrode signal has been analyzed after a step change of . This step response may be approximated by a sum of three exponential functions. Knowing the dynamic behaviour, the transfer function is formulated mathematically and a special analog circuit is constructed with a frequency response inverse to the frequency response of the electrode. Using this device the response time (T ₉₅) of the electrode system is diminished from 11,5 s to 750 ms after a step change of in gas (Luttmann, et al., 1974). If the time for the hydration of CO₂ is decreased by the addition of carbonic anhydrase the response time of the electrode is diminished to 6.5 s. Using the analog circuit yields a response time of 200 ms.Further studies were made to analyze the transient response in fluids at various flow velocities and various mountings. In order to analyze the influence of the fluid boundary layer on the surface of the electrode a photometric method has been developed (Luttmann and Mückenhoff, 1975), which allows to estimate the time course of the CO₂ partial pressure independently of and simultaneously with the electrode measurement.The experimental data are compared with a theory based on theoretical considerations of Schuler and Kreuzer (1967) and Crank (1956).List of Symbols A _i gain factor of thei-th compartment - A _i gain factor of the simulation network - C _i capacity - D diffusion coefficient - d electrode diameter - fraction of CO₂ - F _c (j) frequency response of the linearizing network - F _g (j) frequency response of the boundary layer - F _M (j) frequency response of the measuring system - F _M frequency response of the simulation network - I _i impedance transformer - j Gauss number (j ²=–1) - (j) frequency function of the CO₂ partial pressure - (t) time function of the CO₂ partial pressure - R _i electrical resistance - T _i time constant of the electrode - T _i time constant of the simulation network - T ₉₅ time for reaching 95% of the total difference - V voltage gain factor - v velocity of the streaming fluid - x coordinate - x(t) time function - X(j) corresponding frequency function - dilution factor - inverse time constant - thickness of boundary layer - ^* kinematic viscosity - thickness of diffusion layer - radian frequency Supported by the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 114 (Bionach)     

Adaptive changes in hypercapnic ventilatory response during training and detraining

Summary To confirm the effects of physical training and detraining on CO2 chemosensitivity, we followed hypercapnic ventilatory response at rest in the same five subjects during pre-, post- and detraining for 6 years. They joined our university badminton teams as freshmen and participated regularly in their team's training for about 3 h a day, three times a week, for 4 years. After that they retired from their teams and stopped training in order to study in the graduate school for 2 years. Maximum pulmonary ventilation and maximal oxygen uptake for each subject were determined during maximal treadmill exercise. The slope (S) of ventilatory response to carbon dioxide at rest was measured by Read's rebreathing method. Mean values of increased statistically during training and decreased statistically during detraining. A similar tendency was observed in . The average value ofS before training was 1.91 l·min^–1·mmHg^–1, (+) SD 0.52 and it decreased gradually with increasing training periods; the difference between theS values before (1980) and after training (1982, 1983 and 1984) were all significant. Furthermore, the mean values ofS increased significantly during detraining as compared with those obtained at the end of training (April 1984). We concluded that in normal subjects, long-term physical training increases aerobic work capacity and decreases CO₂ventilatory responsiveness, and that the ventilatory adaptations with training observed here are reversible through detraining.     

Central hypoxic-hypercapnic interaction in mild hypoxia in man

Hypoxic-hypercapnic interaction in mild hypoxia was studied in 12 healthy males. Steady state ventilatory responses to hypercapnic-hypoxia were obtained as the difference in ventilation between hypoxia (mean values ± S.D. of =7.36±0.20 kPa or of 7.10 ±0.41 kPa) and hyperoxia ( >26.7 kPa) with the same degree of hypercapnia ( 6.12±0.22 kPa). On the other band, withdrawal responses were obtained as the magnitude of depression in ventilation caused by two bicaths of O₂ from the above mentioned hypoxic hypercapnia. Averaged and were 9.57±5.45 and 6.45 ±4.90l/min, respectively, the difference being statistically significant (P<0.01). Furthermore, if we assume the presence of ventilatory depression to be due to tissue fall resulting from an increase in cerebral blood flow caused by hypoxia, the magnitude of central hypoxic-hypercapnic interaction was estimated to be as great as the value of .     

Cardiac output in paraplegic subjects at high exercise intensities

Summary The purpose of this investigation was to compare cardiac output ( _c ) in paraplegic subjects (P) with wheelchair-confined control subjects (C) at high intensities of arm exercise. At low and moderate exercise intensity _c was the same at a given oxygen uptake ( O₂) in P and C. A group of 11 athletic male P with complete spinal-cord lesions between T6 and T12 and a group of 5 well-matched athletic male C performed maximal arm-cranking exercise and submaximal exercise at 50%, 70% and 80% of each individual's maximal power output (W_max) . Maximal O₂ ( O_2max) was significantly lower, O_2max per kilogram body mass was equal and maximal heart rate (f _c) was significantly higher in P compared to C. At O₂ of 1.3, 1.5 and 1.7 1-min^–1, and for P 65%–90% of the O_2max, _c was not significantly different between the groups, although, _c in P was achieved with a significantly lower stroke volume (SV) and a significantly higherf _c. Although the SV was lower in P, it followed the same pattern as SV in C during incremental exercise, i.e. an increase in SV until about 45%W _max and thereafter a stable SV. The similar _c at a given O₂ in both groups indicated that, even at high exercise intensities, circulation in P can be considered isokinetic with a complete compensation byf _c for a lower SV.     

The influence of changes inp_{CO_2 } on the fractional packed cell volume of whole blood

In order to investigate the influence of changes in on the fractional packed cell volume (FPCV, hematocrit) of whole blood, a device for measuring the conductivity was developed. This method allows an instantaneous and continous determination of the FPCV, because the erythrocyte membrane has insulating properties, and, consequently, the resistance of blood depends on the relative cell volume. The steady state and transient relationships between FPCV and acid-base levels were investigated by combining this method with simultaneous recordings of .The experiments showed that addition of CO₂ caused an increase in the resistance of whole blood, whereas the resistance of separated plasma decreased slightly and the resistance of true plasma remained almost constant. The change in the FPCV (H) can be described by a linear function of pH or log The transient response of the resistance, after a stepwise increase in the CO₂ content, was found to be the slowest process in attaining an acid-base equilibriu. In blood with acetazolamide, the time courses of changes in pH and were retarded, whereas the time course of the resistance change reflecting the swelling of the erythrocytes was nearly the same (T ₅₀4 s). This may indicate a rate-limited water shift due to a slight water permeability of the erythrocyte membrane.Supported by the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 114 (Bionach)     

Changes of ventilation and ventilatory response to hypoxia during the menstrual cycle

The relationship between change in hypoxic sensitivity in respiration, defined as increment in ventilation per drop of arterial O₂ saturation , with the phase change from follicular to luteal and those in resting pulmonary ventilation , mean inspiratory flow (V _T/T _I), alveolar partial pressures of CO₂ and O₂ ( and , respectively) and body temperature was studied in 10 women. There was a significant relationship between % increase in hypoxic sensitivity and decrement of resting that occurred in the luteal phase. However, no significant relationships were observed between change in hypoxic sensitivity and those in the remaining parameters studied. The intersubject variation in % increase in resting during the luteal phase was not associated with that in % increase in hypoxic sensitivity. The results indicate that the contribution of increased hypoxic sensitivity to increasing during the luteal phase is variable among subjects. Reasons for the increase in hypoxic sensitivity with hypocapnia are discussed.     

O2 Uptake in hyperthyroidism during constant work rate and incremental exercise

Summary To investigate the effect of hyperthyroidism on the pattern and time course of O₂ uptake ( O₂) following the transition from rest to exercise, six patients and six healthy subjects performed cycle exercise at an average work rate (WR) of 18 and 20 W respectively. Cardiorespiratory variables were measured breath-by-breath. The patients also performed a progressively increasing WR test (1-min increments) to the limit of tolerance. Two patients repeated the studies when euthyroid. Resting and exercise steady-state (SS) O₂ (ml·kg^–1·min^–1) were higher in the patients than control (5.8, SD 0.9 vs 4.0, SD 0.3 and 12.1, SD 1.5 vs 10.2, SD 1.0 respectively). The increase in O₂ during the first 20 s exercise (phase I) was lower in the patients (mean 89 ml·min^–, SD 30) compared to the control (265 ml·min^–1, SD 90), while the difference in half time of the subsequent (phase 11) increase to the SS O₂ (patient 26 s, SD 8; controls 17 s, SD 8) were not significant (P = 0.06). The OZ cost per WR increment ( O₂/WR) in ml·min^–1·^–1, measured during the incremental period (mean 10.9; range 8.3–12.2), was always within two standard deviations of the normal value (10.3, SD 1). In the two patients who repeated the tests, both the increment of O₂ from rest to SS during constant WR exercise and the O₂/WRs during the progressive exercise were higher in the hyperthyroid state than during the euthyroid state. While both resting and exercise O₂ are increased in the hyperthyroid patients, the O₂ cost of a given increment of WR is within the normal range. However, a small reduction in the O₂ requirement to perform exercise following treatment of the hyperthyroid state suggests a subtle change O₂ cost of muscle work in this disease.     

Prior heavy knee extension exercise does not affect $$\dot{V}\hbox{O}_{2}$$ kinetics during subsequent heavy cycling exercise

This study examined the magnitude of the oxygen uptake slow component during heavy exercise when preceded by heavy knee extension (KE) exercise. Nine males (26.6 ± 1.7 years, ±SE) performed repeated bouts of heavy exercise, each lasting 6 min with 6 min of recovery. Cycling–cycling trials (CYC₁, CYC₂) involved step transitions to a workrate corresponding to 50% of the difference between peak and the lactate threshold (Δ 50%). During bilateral KE-cycling trails (KE, CYC₃), KE was performed at an intensity requiring twofold greater muscle activation relative to CYC₁ followed by a cycling transition to Δ 50%. was measured breath-by-breath and was modeled using three exponentials to determinate the amplitudes (A ₂′, A ₃′) and time constants (τ ₂, τ ₃) of the primary phase and SC. Electromyography (EMG) recorded from the vastus lateralis and medialis was averaged and reported relative to maximal voluntary contraction (%MVC). EMG was higher (p < 0.05) during KE (37.6 ± 8.1 %MVC) than CYC₁ (20.8 ± 1.9 %MVC), CYC₂ (21.6 ± 5.7 %MVC) and CYC₃ (19.8 ± 6.3 %MVC). The amplitude of the SC was lower (p < 0.05) in CYC₂ (197 ± 120 ml min⁻¹) and CYC₃ (163 ± 51 ml min⁻¹) compared to CYC₁ (325 ± 126 ml min⁻¹). No difference in SC was observed between CYC₂ and CYC₃. Although the activation of additional motor units during KE exercise reduced the amplitude of the SC, the decrease was similar to that observed following heavy cycling exercise. Thus, the activation of motor units in excess of those required for the activity does not alter the response during a subsequent bout of exercise.     

Prognostic value of end-tidal CO<Subscript>2</Subscript> pressure during exercise in patients with left ventricular dysfunction

We compared the prognostic power of end-tidal CO₂ pressure (PETCO₂) during exercise, an index of arterial CO₂ pressure, with those of established respiratory gas indexes during exercise testing in patients with left ventricular dysfunction. Seventy-eight consecutive patients with a left ventricular ejection fraction (LVEF) ≤40% were enrolled in the study. All the patients performed a symptom-limited incremental exercise test with respiratory gas measurements. PETCO₂ at peak exercise, peak O₂ uptake (O₂), the ratio of the increase in ventilation to the increase in CO₂ output (E/CO₂ slope), and the ratio of the increase in O₂ to the increase in work rate (∆O₂/∆WR) were measured. PETCO₂ at peak exercise was significantly correlated with peak O₂, E/CO₂ slope and ∆O₂/∆WR. During a prospective follow-up period of 992 ± 570 days, 14 cardiac deaths occurred. As compared to survivors, non-survivors had a significantly lower LVEF, lower PETCO₂ at peak exercise, lower peak O₂, lower ∆O₂/∆WR and a higher E/CO₂ slope. Among these indexes, only PETCO₂ at peak exercise was found to be an independent predictor for cardiac death. PETCO₂ at peak exercise is useful in predicting poor prognosis in patients with left ventricular systolic dysfunction.     

The effect of exercise intensity and duration on the oxygen deficit and excess post-exercise oxygen consumption

Summary Nine males with mean maximal oxygen consumption ( ) =63.0 ml· kg^–1 · min^–1, SD 5.7 and mean body fat = 10.6%, SD 3.1 each completed nine counterbalanced treatments comprising 20, 50 and 80 min of treadmill exercise at 30, 50 and 70% . The OZ deficit, 8 h excess post-exercise oxygen consumption (EPOC) and EPOC:O₂ deficit ratio were calculated for all subjects relative to mean values obtained from 2 control days each lasting 9.3 h. The O₂ deficit, which was essentially independent of exercise duration, increased significantly (P<0.05) with intensity such that the overall mean values for the three 30%, 50% and 70% workloads were 0.83, 1.89 and 3.09 l, respectively. While there were no significant differences (P>0.05) between the three EPOCs after walking at 30% for 20 (1.01 l), 50 (1.43 l) and 80 min (1.041), respectively, the EPOC thereafter increased (P<0.05) with both intensity and duration such that the increments were much greater for the three 70% workloads (EPOC: 20 min=5.68 l; 50 min=10.04 l; 80 min= 14.59 l) than for the three 50% workload (EPOC: 20 min =3.14 l; 50 min=5.19 l; 80 min= 6.10 l). An analysis of variance indicated that exercise intensity was the major determinant of the EPOC since it explained five times more of the EPOC variance than either exercise duration or the intensity times duration interaction. The mean EPOC:O₂ deficit ratio ranged from 0.8 to 4.5 and generally increased with both exercise intensity and duration. These data imply that the EPOC is more than mere repayment of the O₂ deficit because metabolism is increasingly disturbed from resting levels as exercise intensity and duration increase due to other physiological factors occurring after the steady-state has been attained.     

Use of oxygen uptake recovery curve to predict peak oxygen uptake in upper body exercise

A group of 18 well-trained white-water kayakers performed maximal upper body exercise in the laboratory and during.a field test. Laboratory direct peak oxygen uptake ( ) values were compared, firstly by a backward extrapolation estimation and secondly by an estimation calculated from measured during the first 20 s of exercise recovery. Direct peak correlated with backward extrapolation (r=0.89), but the results of this study showed that the backward extrapolation method tended to overestimate significantly peak by [0.57 (SD 0.31) 1·min^–1 in the laboratory, and 0.66 (SD 0.33) 1·min^–1 in the field,P<0.001]. The measured during the first 20 s of recovery, whether the exercise was performed in the laboratory or in the field, correlated well with the laboratory direct peak (r=0.92 andr=0.91, respectively). The use of the regression equation obtained from field data _2f20s, that is peak ₂=0.23+1.08 _2f20s, gave an estimated peak ₂, the mean difference of which compared with direct peak was 0.22 (SD 0.13) 1·min^–1. In conclusion, we propose the use of a regression equation to estimate peak from a single sample of the gas expired during the first 20 s of recovery after maximal exercise involving the upper part of the body.     

Influence of hepatic innervation on renal glomerular filtration rate

Electrical stimulation of perivascular portal nerves leads to rapid, transient increase of renal glomerular filtration rate (GFR) and of urinary flow rate ( ). In contrast, perivascular stimulation at the vena cava inferior does not significantly alter GFR and . Spinal transfection at the thoracocervical junction does not significantly modify the effect of periportal nerve stimulation. Infusion of the -adrenergic agonist phenylephrine (20 nmol/min) into the superior mesenteric vein increases GFR and , whereas infusion of identical amounts of phenylephrine (20 nmol/min) into the jugular vein does not significantly alter GFR or . The observations indicate that -adrenergic innervation of the liver modifies renal function.