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J Porszasz

Publications and source records attributed to J Porszasz.

10 recordsLinked to original sources
PubMed2001

Dose-response effect of oxygen on hyperinflation and exercise endurance in nonhypoxaemic COPD patients.

Dynamic hyperinflation contributes to exertional breathlessness and reduced exercise tolerance in chronic obstructive pulmonary disease (COPD) patients. This study examined whether oxygen supplementation results in a dose-dependent decrease in hyperinflation associated with functional and symptomatic improvement. Ten severe COPD patients without clinically significant oxygen (O2) desaturation during exercise, and seven healthy subjects, performed five exercise tests at 75% of maximally tolerated work rate. Inspired oxygen fraction (FI,O2) was varied (0.21, 0.3, 0.5, 0.75 and 1.0) among tests in a randomized order. Ventilation (V'E) was measured, and end-inspiratory (EILV) and end-expiratory (EELV) lung volume changes were assessed from inspiratory capacity manoeuvres. In the patients, compared to room air, endurance time increased with FI,O2=0.3 (mean+/-SEM 92+/-20%) and increased further with FI,O2=0.5 (157+/-30%). At isotime, compared to room air, there were significant reductions in dyspnoea score, EELV, EILV, V'E and respiratory frequency (fR) with FI,O2=0.3. Improved endurance time negatively correlated with change in EELV (r=0.48, p=0.002) and EILV (r=0.43, p=0.005). The dyspnoea rating decrease correlated with fR decrease. In healthy subjects, smaller V'E and fR decreases were observed at FI,O2=0.5, accompanied by more modestly increased endurance. Oxygen supplementation during exercise induced dose-dependent improvement in endurance and symptom perception in nonhypoxaemic chronic obstructive pulmonary disease patients, which may be partly related to decreased hyperinflation and slower breathing pattern. This effect is maximized at an inspired oxygen fraction of 0.5.

Aged↗
PubMed1998

Exercise tolerance in asymptomatic elderly men with fluoroscopically detected coronary artery calcification.

STUDY OBJECTIVE: The value of detecting coronary artery calcification (CAC), by cardiac imaging, for the diagnosis of coronary artery disease (CAD) in asymptomatic middle-aged men has been demonstrated. However, the incidence of CAC increases with age. The functional significance of CAC remains unknown in asymptomatic elderly men. The purpose of this study is to explore whether CAC in asymptomatic aging men signifies the presence of cardiovascular dysfunction during exercise. DESIGN: This study was designed to address whether elderly asymptomatic men, selected because they have CAC, have reduced exercise tolerance due to functionally significant CAD. PARTICIPANTS AND SETTING: Thirty-eight asymptomatic male volunteers (ages 50 to 75 years, mean [+/-SD] 64+/-7 years) with a normal resting ECG and at least one coronary risk factor, in a population study. Nineteen subjects had CAC detected by digital subtraction fluoroscopy in at least two major coronary arteries, and 19 subjects had no identifiable CAC. METHODS AND RESULTS: Each subject underwent a symptom-limited incremental exercise test with 12-lead ECG monitoring and respiratory gas analysis. Four indexes of exercise oxygen transport were evaluated: peak oxygen uptake (VO2), lactic acidosis threshold, peak VO2/heart rate ratio, and VO2 relative to a work rate increase. Eleven of 38 subjects (28%) were found to have reduced oxygen transport, which was defined as an abnormal reduction in more than two of the above four indexes of oxygen transport. Five of the 11 subjects with reduced oxygen transport had CAC, and 6 subjects did not (not significant). Only one subject with CAC had exercise ST depression. CONCLUSION: Significant CAC in asymptomatic men over age 50 does not signify exercise limitation due to CAD.

Aged↗
PubMed1997

Physiologic benefits of exercise training in rehabilitation of patients with severe chronic obstructive pulmonary disease.

We determined the effect on exercise tolerance and physiological exercise responses of rigorous rehabilitative exercise training in chronic obstructive pulmonary disease (COPD). Fifteen men and 10 women (mean age, 68 +/- 6 yr; FEV1, 0.93 +/- 0.27 L) participated in a rehabilitation program with an exercise component of three per week 45-min sessions of cycle ergometer training for 6 wk with exercise intensity kept near maximal targets. Before and after rehabilitation, patients performed an incremental test and a constant work rate (CWR) test at 80% of the peak work rate in the preprogram incremental test. Ventilation (V(E)) and gas exchange were measured breath by breath; arterialized venous blood was analyzed for blood gas determinations and lactate. Rehabilitation yielded an average increase in peak work rate in the incremental test of 36% (p < 0.001), and in the duration of the CWR test of 77% (p < 0.001). In the CWR test, the kinetics of O2 uptake, CO2 output, V(E), and heart rate were markedly slower than those of healthy subjects. After training, mean response time decrease averaged 17, 22, 34, and 29%, respectively (p < 0.02), evidence of a physiologic training effect. Further, for identical CWR tasks, V(E) was 10% lower (p < 0.02) after training, attributable to altered breathing pattern: tidal volume increased by 8% and respiratory rate decreased by 19%, yielding lower V(D) /V(T) (0.46 versus 0.53 p < 0.005). Rigorous exercise training for patients with severe COPD yields more efficient exercise breathing pattern and lower V(E); this is associated with improved exercise tolerance.

Aged↗
PubMed1996

Effects of hypoxic hypoxia on O2 uptake and heart rate kinetics during heavy exercise.

It is unclear whether hypoxia alters the kinetics of O2 uptake (VO2) during heavy exercise [above the lactic acidosis threshold (LAT)] and how these alterations might be linked to the rise in blood lactate. Eight healthy volunteers performed transitions from unloaded cycling to the same absolute heavy work rate for 8 min while breathing one of three inspired O2 concentrations: 21% (room air), 15% (mild hypoxia), and 12% (moderate hypoxia). Breathing 12% O2 slowed the time constant but did not affect the amplitude of the primary rise in VO2 (period of first 2-3 min of exercise) and had no significant effect on either the time constant or the amplitude of the slow VO2 component (beginning 2-3 min into exercise). Baseline heart rate was elevated in proportion to the severity of the hypoxia, but the amplitude and kinetics of increase during exercise and in recovery were unaffected by level of inspired O2. We conclude that the predominant effect of hypoxia during heavy exercise is on the early energetics as a slowed time constant for VO2 and an additional anaerobic contribution. However, the sum total of the processes representing the slow component of VO2 is unaffected.

Adult↗
PubMed1995

Changes in skeletal muscle oxygenation during incremental exercise measured with near infrared spectroscopy.

To determine the change in muscle oxygenation in response to progressively increasing work rate exercise, muscle oxyhemoglobin + oxymyoglobin saturation was measured transcutaneously with near infrared spectroscopy in the vastus lateralis muscle during cycle ergometry. Studies were done in 11 subjects while gas exchange was measured breath-by-breath. As work rate was increased, tissue oxygenation initially either remained constant near resting levels or, more usually, decreased. Near the work rate and metabolic rate where significant lactic acidosis was detected by excess CO2 production (lactic acidosis threshold, LAT), muscle oxygenation decreased more steeply. As maximum oxygen uptake (VO2max) was approached, the rate of desaturation slowed. In 8 of the 11 subjects, tissue O2 saturation reached a minimum which was sustained for 1-3 min before VO2max was reached. The LAT correlated with both the VO2 (r = 0.95, P < 0.0001) and the work rate (r = 0.94, P < 0.0001) at which the rate of tissue O2 desaturation accelerated. These results describe a consistent pattern in the rate of decrease in muscle oxygenation, slowly decreasing over the lower work rate range, decreasing more rapidly in the work rate range of the LAT and then slowing at about 80% of VO2max, approaching or reaching a minimum saturation at VO2max.

Acidosis, Lactic↗
PubMed1995

The level and tempo of children's physical activities: an observational study.

We develop an observation system that quantifies the duration, intensity, and frequency of children's physical activities. We use this system to assess the level and tempo of energy expenditure under free-ranging, natural conditions experienced by 15 children aged 6-10 yr in southern California. Observations were recorded every 3 s during 4-h time blocks from 8:00 a.m.-8:00 p.m. Agreement among observers using the coding system was 91%. Using indirect calorimetry, calibration studies in the laboratory determined VO2 (ml.min-1.min-1) during each coded activity, and activities were categorized by intensity (low, medium, or high). Subjects were found to engage in activities of low intensity 77.1% of time and activities of high intensity 3.1% of time. The median duration of low and medium intensity activities was 6 s, of high intensity activities only 3 s with 95% lasting less than 15 s. Children engaged in very short bursts of intense physical activity interspersed with varying intervals of low and moderate intensity. These findings may be important for discovering how children's activity patterns under natural conditions influence physiological processes leading to growth and development. This study demonstrates the advantages of using an observational system that captures more than the intensity and frequency of children's activities to include duration and the length of intervals between activities of varying intensity.

Child↗
PubMed1995

Skeletal muscle oxygenation during constant work rate exercise.

We compared the slow rise in VO2 during heavy exercise (i.e., greater than lactic acidosis threshold (LAT)) with changes in muscle oxyhemoglobin+oxymyoglobin (O2Hb/O2Mb) saturation by reflectance near infrared spectroscopy. Ten subjects performed four 6-min cycle ergometer tests with two constant work rates less than and two greater than the LAT, equivalent to 20, 40, 65 and 75% peak VO2. During less than LAT exercise, O2Hb/O2Mb saturation decreased to a minimum by 2 min and then remained constant or rose slightly. For greater than LAT work rates, the initial fall in O2Hb/O2Mb saturation was greater the higher the work rate and continued to decrease with time after 3 min. Between minutes 3 and 6, the rate of decrease in O2Hb/O2Mb saturation correlated with the increase in VO2 (r = -0.69, P < 0.0001). These studies support the hypothesis that the slow rise in VO2 during heavy constant work rate exercise is associated with a progressive decline in O2Hb/O2Mb saturation in the contracting muscles themselves that may be facilitated by capillary oxyhemoglobin dissociation owing to tissue lactic acidosis (Bohr effect).

Adult↗
PubMed1994

Evaluation of a symmetrically disposed Pitot tube flowmeter for measuring gas flow during exercise.

We evaluated the effect of airflow and gas composition on the linearity of measurement of airflow by a new disposable flowmeter. The flowmeter is based on the principle of differential pressure measurement across two symmetrically disposed Pitot tubes. Nonlinearities arising from the pressure-to-airflow relationship and sensitivity to changes in gas density were linearized with appropriate software and monitoring of the gas composition. With room air used as the respired gas, the measured tidal volume from a piston pump assembly was consistently within 1-2% of the target tidal volume for each of five flowmeters tested across physiological ranges of flow. Changing gas densities by varying concentrations of O2, CO2, and N2 led to errors in tidal volume measurement that ranged up to 6-8%. However, because the errors were predictable, they were corrected by software to within 0.6% of the target volume. Measurement of minute ventilation during exercise was within 1-2% of that determined from bag collections. We conclude that this type of flowmeter can accurately measure exercise minute ventilation and has advantages over some other flowmeters because of its ruggedness, reproducibility, and ease of sterilization or replacement compared with other flowmeters.

Equipment Design↗
PubMed1993

Femoral vascular occlusion and ventilation during recovery from heavy exercise.

Ventilation and cardiac output subside gradually following cessation of exercise, which is commonly linked to the slow wash-out of materials from the recovering muscles. The effect of hindering the removal of the metabolic products of heavy cycle exercise on the kinetics of ventilation and gas exchange was studied in 5 subjects by occluding the femoral circulation with cuffs during the first 2 min of recovery (15 tests). Fifteen undisturbed recoveries served as controls. Compared to spontaneous recovery, circulatory obstruction induced an immediate (from the first breath) decrease in minute ventilation (VE), while end-tidal CO2 (PETCO2) as well as lactate and K+ in venous blood at forearm did not change significantly. A ventilatory deficit of 27 +/- 9 L was observed from the 2 min of occlusion. Following cuff deflation, VE rose 2-3 breaths after PETCO2 began to increase in every subject. The mechanisms of the normocapnic reduction of VE during occlusion, as well as the rise of ventilation following cuff release, are still unclear. However, these results argue against any significant role for hyperpnea-inducing intramuscular chemoreception, or point to muscular perfusion as a prerequisite of such a mechanism to operate.

Adult↗