Reliability of a new device to assess the oxygen consumption of human respiratory muscles.

PURPOSE: This study tests the reliability of a new device for assessing the oxygen consumption of the respiratory muscles (VO2 resp.). METHODS: Fourteen healthy male volunteers participated in the study. The device consists of an expandable external ventilatory dead space created with pieces of plastic tubing and a spirometer filled with 100% oxygen. It also incorporates a carbon dioxide absorber. Total VO2 (VO2 tot.) was recorded from the spirometric closed circuit and ventilation (V(E)), from the spirometer tracing. For each subject the test procedure was carried out in duplicate (T1 and T2) after an overnight fast. The dead space was increased at a constant rate of 260 mL every 90 s, and VO2 tot. and V(E) increased progressively. Because log VO2 tot. was linearly related to V(E), we calculated the slope value (log VO2-V(E)) and the Y-intercept (VE = 0) of the semilog regression representing, respectively, VO2 resp. and metabolic VO2 (VO2 met.). RESULTS: When compared with values in the literature, these values did not differ from those recorded in subjects of a similar age group. The VO2 resp. and VO2 met. calculated in T1 and T2 were not different (VO2 resp. = 0.0066 +/- 0.0005 for T1 vs 0.0067 +/- 0.0005 log mL x min(-1)/L x min(-1) for T2 and VO2 met. = 269.3 +/- 28.6 for T1 vs 281.9 +/- 24.1 mL x min(-1) for T2). The coefficients of variation were: 25% at T1 and 23% at T2 for VO2 resp. and 34% at T1 and 29% at T2 for VO2 met. Moreover, significant correlations (r = 0.96, P < 0.001 for VO2 resp., r = 0.95, P < 0.001 for VO2 met.), high coefficients of determination (r2 = 0.92 for VO2 resp., r2 = 0.90 for VO2 met.) and negligible SEE (0.0005 for VO2 resp., 0.2 mL x min(-1) for VO2 met.) were found between the two tests. When we plotted the mean values of VO2 resp. and VO2 met. measured at T1 and T2 against their respective differences, more than 95% of the slight differences ranged between the limits defined by mean value +/- 2 SD, reflecting the small discrepancy between duplicate measurements. CONCLUSION: The results confirm that the test performed with this device is useful and reliable for assessing the VO2 resp. in healthy subjects.

Measurement of functional residual capacity through the transient phase of He dilution in newborns.

Helium dilution maneuver is used to determine the functional residual capacity (FRC) 14 newborns ages 1-5 mo. The model equation describes the changing alveolar fractions of He and the ventilation promoted by a rebreathing procedure that does not exceed 40 s. The model does not involve the volume of the rebreathing bag usually needed when applying rebreathing technique and which is a source of error. The equation is discretized and solved for recorded data obtained with equipment adapted to newborns. Results show a strong relationship between FRC and the biometrical indexes, and confirm those found in the literature featuring that the measurement duration of FRC can be considerably shortened.

Determination of diffusing capacity by modeling the dynamics of C18O uptake in newborns.

Dynamic modeling of lung C18O diffusion is used to measure the C18O transfer factor (TLCO) of 14 newborns aged 1-4 mo. The model equation is based on the alveolar fractions of C18O and on changing alveolar ventilation induced by the rebreathing conditions. The model does not involve the volume of the rebreathing bag which is usually needed when applying rebreathing technique and which is a source of error. The equation is discretized and solved for recorded data obtained with equipment adapted to use in newborns. A least-square parameter calculation technique is applied to estimate TLCO. Results show a strong relationship between this index and the biometrical ones and confirm those found in the literature featuring that the measurement duration can be considerably shortened.

Maximal oxygen uptake and aerobic-anaerobic transition on treadmill and bicycle in triathletes.

The maximal aerobic capacity and the aerobic-anaerobic transition were analyzed on 14 triathletes performing an incremental work load on a bicycle ergometer and on horizontal or inclined treadmills. To compared the cardiorespiratory responses between cycling and running, the subjects were divided into 2 groups of 7 with similar aerobic capacity determined from cycle runs. The first group ran on horizontal treadmill while the second group performed similar exercise on inclined treadmill at constant grade (1.5%). Heart rate was recorded by electrocardiogram. Oxygen uptake (VO2), CO2 production (VCO2), respiratory frequency, and pulmonary ventilation were monitored at 30 s intervals through a Rudolph valve connected to a calibrated Oxycon V. Tidal volume, respiratory exchange ratio, equivalent O2 and CO2 were calculated from on-line computer. Aerobic and anaerobic thresholds were determined by a non-invasive method from pulmonary ventilation curves. The results showed that maximum oxygen uptake (VO2max) did not differ between the 2 types of ergometers. Pulmonary ventilation, heart rate and VO2 recorded at aerobic and anaerobic thresholds depended on the mode of exercise and reached the highest values on inclined treadmill. The amount of muscle mass, the type and the distribution of active motor units involved in each exercise test might be at the origin of these differences. This indicates that, when assessing a training program from anaerobic threshold values, it is necessary to take into consideration the type of ergometer used and the protocol performed.

Aerobic capacity of competitive ice hockey players 10-15 years old.

Oxygen uptakes (VO2) recorded at anaerobic threshold and at the end of a maximal exercise (VO2 max) and their relation to left ventricular function were analyzed in 11 young ice hockey players during an incremental exercise on a bicycle ergometer. The children, highly trained, participated annually during 6 years (from the age of 10-15 years) in laboratory tests. The maturative status of the subjects was evaluated from peak height velocity (PHV). Heart rate was recorded by electrocardiogram. Oxygen uptake, CO2 production, respiratory frequency, pulmonary ventilation (VE) were recorded at rest and every 30 s during exercise through a Rudolph valve connected to a calibrated oxycon gas analyser. The anaerobic threshold was determined by a non-invasive method from pulmonary ventilation curves. Left ventricular volumes at end-systole and end-diastole were obtained, at rest, by M mode echocardiography. Results showed that both VO2 at anaerobic threshold and VO2max were positively correlated with body mass or with age of PHV. The increments were constant from year to year. At anaerobic threshold, the ratio VO2/VO2max was independent of maturative age. Similar findings were observed when considering VE except after the years of PHV where there was a remarkable increase in pulmonary ventilation. The results indicate that the growth of each cardiorespiratory component is optimalized with body size increase in order to keep constant the aerobic response to exercise. As judged by the explained variance of the different linear regression analyses between resting left ventricular dimensions and VO2, cardiac volume was of minimal importance in determining VO2. In the postpubertal period, stroke volume accounted for 26.7% of VO2 at anaerobic threshold and 30.0% of VO2max. This suggests that local changes occurring at muscular level are of paramount importance in determining the aerobic capacity of highly trained boys.

[Peripubertal longitudinal study by echocardiography of left heart development in a group of ice hockey players]. / Etude longitudinale péripubertaire, par échographie, du développement cardiaque gauche d'un groupe de hockeyeurs sur glace.

The modalities of left ventricular (LV) adaptation (dilatation and/or hypertrophy) to exercise are not as well known in children as in adults. Therefore, the authors followed up 11 national ice hockey players, initially aged 10, following an eight hour per week training schedule for a period of 5 years. M mode echocardiographic studies were carried out each year during the training period to measure LV internal dimensions, wall thickness, myocardial mass and contractility (fractional shortening and systolic stress index). The evolution of these parameters was evaluated (Student's test) by two year peripubertal periods (10-12 years: 12-14 years) and compared in absolute values and in rate of growth with the standardised values indexed to body surface area reported by Henry. Between 10 and 12 years of age, the LV internal dimensions (a good indicator of LV volume in healthy children) increased significantly (p less than 0.05) and LV mass increased very significantly (p less than 0.01). The LV internal dimensions were normal at the outset and remained in the upper limits of normality reported by Henry with a normal rate of growth. Myocardial mass was normal at the age of 10 and its rate of growth was also normal. Between 12 and 14 years of age, the increase in LV internal dimensions was not statistically significant but myocardial mass increased very significantly (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Neonatal thermoregulation.

The human being is a homeotherm. Homeothermy is a result of thermoregulation which includes many physiological processes. Thermoregulation maintains an equilibrium between heat production (thermogenesis) and heat loss (thermolysis). There are three principal modes of heat production: 1. Voluntary muscle activity. 2. Involuntary tonic or rhythmic muscle activity known as "shivering". 3. Non-shivering thermogenesis (NST) essential for newborns. Heat loss occurs in two stages: 1. The flow of heat from the center of the body to its surface. 2. The flow of heat from the body surface to the environment by conduction, convection, radiation or water evaporation. Even in the very small premature baby, we find that metabolic and vasomotor control responses are developed. To protect the newborn from stress resulting from hypo or hyperthermia, one should take into consideration the concept of the neutral temperature range which is also called the "Thermoneutral Zone" in (TNZ) or "Thermal Neutrality". Curves, proposed in 1971 by Hey are essential for keeping newborns in the TNZ.

[Evolution of the result of respiratory function studies in children with bronchopulmonary dysplasia]. / Evolution du résultat des explorations fonctionnelles respiratoires chez les enfants atteints de dysplasie bronchopulmonaire.

BACKGROUND: Reports of short- and medium-term evolution of Lung Function Tests (LFT) in infants with bronchopulmonary dysplasia (BPD) are still scarce. POPULATION AND METHODS: The results of the first (before 3 months of corrected age) and the second (between 3 and 9 months of corrected age) LFT in 22 premature infants with BPD (gestational age 31 +/- 2.5 weeks; birth weight: 1570 +/- 440 g; duration of mechanical ventilation: 46 +/- 24 days, total duration of oxygen therapy: 88 +/- 47 days) were compared to those obtained in 27 normal infants for the first LEF and 10 normal infants for the second LFT, similar to the patients for birth weight and corporeal index (CI). RESULTS: In the first LFT, major abnormalities were an increased thoracic gaz volume (TGV) (16.5 +/- 42 vs 122 +/- 24 mL; P < 0.001) and TGV CI ratio (1.25 +/- 0.31 vs 0.89 +/- 0.17 ml/kg/m2; P < 0.0001) a decreased pulmonary compliance (2.49 +/- 1.46 vs 11.60 +/- 4.50 mL/cmH2O; P < 0.0001) and specific pulmonary compliance (0.015 +/- 0.10 vs 0.100 +/- 0.042 mL/cmH2O/mL de TGV; P < 0.0001), an increased total pulmonary resistance (20.4 +/- 12.1 vs 10.5 +/- 5.3 cmH2O/L/s; P < 0.001). In the second LFT, an increased TGV (235 +/- 62 vs 166 +/- 28 mL; P < 0.01) and TGV CI ratio (1.64 +/- 0.65 vs 0.98 +/- 0.11 ml/kg/m2; P < 0.05), a decreased pulmonary compliance (2.68 +/- 2.0 vs 15.2 +/- 5.7 mL/cmH2O; P < 0.0001) and specific pulmonary compliance (0.013 +/- 0.010 vs 0.106 +/- 0.050 mL/cmH2O/mL de TGV; P < 0.0001), an increased total pulmonary resistance (17.1 +/- 9.6 vs 8.6 +/- 4.9 cmH2O/L/s; P < 0.05) were noted when compared with the control group results. Major abnormalities of the blood gases were hypoxemia (63 +/- 10 vs 85 +/- 20 mmHg; P < 0.05), hypercapnia (38.5 vs 31 +/- 4 mmHg; P < 0.0001) during the first LFT. Hypoxemia (77 +/- 14 vs 90 +/- 14 mmHg and hypercapnia (37 +/- 4 vs 29 +/- 5 mmHg) continued in the second LFT. Thoracic distention and total pulmonary resistances in infants with BPD did not improve but their pulmonary compliance (P < 0.0001) and PaO2 (P < 0.01) between the first and second LFT did it. Infants who had been ventilated for a hyaline membrane disease (HMD) were more hypoxic on the second LFT (P < 0.05) than those who had been ventilated for other causes. Statistically significant relationships were found between thoracic distention and duration of positive inspiratory pressure (P < 0.05; r = 0.43), duration of positive expiratory pressure (P < 0.05, r = 0.45) total oxygen therapy duration; between total pulmonary resistance and duration of mechanical ventilation with high frequency (P < 0.05; r = 0.52); between hypoxemia and duration of oxygen therapy with FiO2 > or = 60% (P < 0.05; r = 0.54). CONCLUSIONS: This study shows prolonged clinical and functional abnormalities of the respiratory functions requiring longer follow-up.

[Study of a new fetal blood gas parameter: oxygen saturation]. / Etude d'un nouveau paramètre des gaz du sang du foetus: la saturation en oxygène.

The oxygen saturation, together with the other parameters of the acid-base balance, was studied in the umbilical vessels of 60 neonates born by vaginal delivery. These assays were used to define the normal range, which is 28 to 38% in the umbilical artery and 62 to 74% in the umbilical vein. The umbilical arterio-venous gradient was always negative. Correlations with the pH and the serum lactate concentration demonstrate that oxygen saturation is a good parameter for the evaluation of foetal hypoxia, which has the advantage of being easily measurable.

The hyperoxic test in infants reinvestigated.

The hyperoxic test (HT) examines peripheral chemoreceptor function (PCF) by measuring the decrease in ventilation (V E) after 100% O(2) inhalation. A 30-s HT has been previously used in infants with calculation of the ventilatory response (VR) as the mean percentage change in V E during HT as compared with normoxia. However, it has been shown that during hyperoxia V E rises secondarily after the initial drop because of loss of PCF. We hypothesized that the mean V E change over a 30-s HT may underestimate the strength of PCF and may be poorly reproducible. We performed breath-by-breath analysis during 30-s HTs, calculating VR at the response time (RT) defined as the time from HT onset to the first significant HT-related change in V E. Eighteen infants (postnatal age, 21 +/- 4 d) underwent two HTs (quiet sleep, face mask attached to a pneumotachograph, and inspired and expired O(2) and CO(2) fractions measured using mass spectrometry). V E, VT, and VT/TI decreases at the RT were significantly greater than the corresponding means (-21 +/- 7 versus -15 +/- 7%, -21 +/- 8 versus -13 +/- 8%, and -22 +/- 11 versus -17 +/- 11%, respectively). Intra-individual coefficients of variation of V E, VT and VT/TI were significantly smaller when RT values were considered rather than means. We conclude that calculation of the VR to HT at RT improves assessment of PCF and enhances HT reproducibility in infants.

Reproducibility of the alternating breath test of fractional inspired O2 in infants.

We conducted a reproducibility study of the alternating breath test (ABT) for assessing peripheral chemoreceptor function in infants. The ABT delivers a rapid hypoxic stimulus to the peripheral chemoreceptors with breath-by-breath alternations of the inspired O2 fraction. The reproducibility of the ABT performed on a single occasion has not been extensively studied in infants. Eight unsedated infants (postnatal age, 22+/-19 d; weight, 3.2+/-0.4 kg) were studied in standardized conditions: morning naps, supine position, room temperature 22-24 degrees C, quiet sleep, and face mask attached to a pneumotachograph connected to a two-way electric valve. Respiratory gases were analyzed by mass spectrometer. Two ABTs were performed. Each included a 2-min control run (CR) alternating between air and air, and a 2-min test run (TR) alternating between air and 0.15 O2. After data preprocessing, on average 13+/-11% of the data were rejected because of sighs, apneas, and cycles with the fraction of inspired oxygen above 0.17. Using the remaining validated breaths, the response to ABT was calculated for the CR, for all breaths in the TR (TR(T)), and for the first 50 breaths of the TR (TR50). During the ABTs oxygen saturation did not fall below 96%, and heart rate was not affected. Inspired and end-tidal CO2 fractions remained unchanged during the ABTs. FetO2 oscillated in TRs at a lower values than in CRs and differed significantly between breaths of air and hypoxic breaths of TRs. All infants responded to ABT with percentage alternation coefficients of TRs significantly greater than those of CRs for all respiratory variables. The values of the coefficients were not significantly different between both ABT, and between TR50 and TR(T). The greatest values of the coefficients were for timing variables compared with flows and volume. We conclude that the ABT is a reproducible test of peripheral chemoreceptor function under standardized conditions.

[Trans-cerebral electric analgesia: reality, hypothesis or placebo? (author's transl)]. / Electro-analgésie transcérébrale: réalité, hypothèse ou placebo?

Sixty patients undergoing major digestive surgery received the same amount of drugs for induction of anesthesia; neuroleptic, morphinomimetic and pachycurares were used and calculated in mg/kg. A randomisation list permitted to define 45 patients who received in double blind (by means of a long electrical cord), an electrical current varying for each protocol; the control group (15 patients) did not receive an electrical current. Statistical study of the amount of drugs used for follow of anesthesia shows no real effect of electrical analgesia for digestive surgery.

Effects of interval training at the ventilatory threshold on clinical and cardiorespiratory responses in elderly humans.

This study assessed clinical and cardiorespiratory responses after an interval training programme in sedentary elderly adults using the ventilatory threshold (Vth) as the index of exercise training intensity. A selection of 22 subjects were randomized into two groups: 11 subjects served as the training group (TG) and the others as controls (CG). Maximal exercise tests were performed on a treadmill before (T0), each month (T1, T2) and after the 3-month interval training programme period (T3). The TG subjects were individually trained at the heart rate corresponding to Vth measured at T0, T1 and T2 as the breakpoint in the oxygen uptake-carbon dioxide production relationship. Their training programme consisted of walking/jogging sessions on a running track twice a week. The sessions consisted of varying durations of exercise alternating with active recovery in such a way that the subjects slowly increased their total exercise time from an initial duration of 30 min to a final duration of 1 h. During training the heart rate was continuously monitored by a cardiofrequency meter. Compared with the daily activities of the controls, no training programme-related injuries were observed in TG. Moreover, programme adherence (73%) and attendance (97.3%) were high. The maximal oxygen uptake and Vth were increased in TG, by 20% (P<0.05) and 26% (P<0.01), respectively. Interval training at Vth also significantly increased maximal O2 pulse (P<0.05) and maximal ventilation (P<0.01). A significant decrease in submaximal ventilation (P<0.05) and heart rate (P<0.01) was also noted. These results would suggest that for untrained elderly adults, an interval training programme at the intensity of Vth may be well-tolerated clinically and may significantly improve both maximal aerobic power and submaximal exercise tolerance.