摘要:

Purpose:Little is known about cardiovascular responses during recovery from exercise in patients with cardiovascular disease. The aim of this study was to determine the time constants of the kinetics of oxygen uptake and heart rate during recovery from exercise and to evaluate the influence of resting cardiac function on these kinetics in patients with left ventricular dysfunction.Methods:A moderate exercise test was performed by 40 patients (57 ± 10 yr old) with prior myocardial infarction at a constant work rate (40 ± 8 W) for 6 min on a cycle ergometer. The time constants of oxygen uptake and heart rate during 6 min of recovery were compared in patients whose left ventricular ejection fractions were ≥35% (group 1,N= 20) and those with ejection fractions <35% (group 2,N= 20).Results:The time constant of the decrease in oxygen uptake during exercise recovery was significantly prolonged (oxygen requirement was increased) in group 2 compared with group 1. Heart rate during recovery was consistently higher, and its time constant was prolonged in group 2 compared with group 1. The time constant of oxygen uptake was positively correlated with the time constant of heart rate.Conclusion:The recovery of oxygen uptake after exercise was significantly delayed, associated with delayed recovery of heart rate, in patients with severely impaired left ventricular function.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Purpose:Although nitrates are known to improve indices of exercise capacity in patients with coronary artery disease, their effects on oxygen uptake kinetics during the onset of exercise have not been clarified. We evaluated the acute effects of isosorbide dinitrate on the kinetics of oxygen uptake during the onset of exercise at a constant work rate in patients with coronary artery disease.Methods:We studied 14 patients with coronary artery disease who performed 6 min of low-intensity exercise at a constant work rate on a cycle ergometer 30 min after oral administration of 10 mg of isosorbide dinitrate or placebo in a double-blind, crossover manner. Oxygen uptake was calculated from breath-by-breath analysis of respired gases. The time constant of oxygen uptake kinetics during the onset of exercise was determined by fitting a single exponential function to the oxygen uptake response.Results:Heart rate was significantly increased at rest, and systolic blood pressure was significantly decreased both at rest and during exercise after administration of isosorbide dinitrate. The time constant of oxygen uptake was significantly shorter (the kinetics were faster) after administration of isosorbide dinitrate (39.4 ± 10.1 vs 44.5 ± 10.5 s,P= 0.038).Conclusions:Isosorbide dinitrate was found to speed the kinetics of the increase in oxygen uptake during constant work-rate exercise. The time constant of oxygen uptake, which reflects the rapidity of cardiovascular adaptation at the onset of exercise, seems to be a useful parameter of the effectiveness of therapy in patients with coronary artery disease.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

The role of ventilation in the response in aerobic capacity and arterial oxygen saturation (SaO2) to acute hypoxic exercise was studied in 13 healthy active men divided into two groups based on their normoxic maximal exercise ˙VE/˙VO2(LOW ≤ 27.7; HIGH ≥ 30.2) and PAO2estimates (LOW ≤ 107 mm Hg; HIGH ≥ 110 mm Hg). Groups performed two incremental progressive maximal cycle exercise(˙VO2max) tests: normoxia (FIO2= 20.9%) and acute hypoxia(FIO2= 13.3%). To evaluate the influence of hypoxic ventilatory drive on ventilation, resting hypoxic ventilatory response (rHVR) was measured. LOW demonstrated lower ventilatory responses (˙VE,˙VE/˙VO2, and ˙VE/˙VCO2) during both normoxic and hypoxic exercise (P≤ 0.05). During maximal hypoxic exercise, LOW had a greater decline in both ˙VO2max(21.6 mL·kg-1·min-1vs 16.6 mL·kg-1·min-1) and SaO2(31.9% vs 22.1%). Modest but significant correlations were identified between normoxic˙VE/˙VO2and the decline in both ˙VO2max(r =-0.62) and SaO2(r = -0.60). No correlations were identified between rHVR and any ventilatory response or SaO2. In summary, the results from this study suggest that a low exercise-induced hyperventilatory response is a significant mechanism in the arterial desaturation observed during hypoxic exercise and the decline in aerobic capacity associated with this desaturation. However, the ventilatory response to hypoxic exercise is not dependent upon hypoxic ventilatory drive.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Herein we describe a new test system to produce a standardized partial muscle-tendon junction (MTJ) stretch injury. In anesthetized rabbits the tibialis anterior (TA) muscle-tendon unit is unilaterally shortened using a custom designed clamp roller system. An angular displacement (average velocity of 450 °·s-1) is applied about the foot to plantarflex the ankle 90 ° while the lower extremity is fixed. During ankle rotation the TA muscle is tetanically stimulated to generate an eccentric stretch injury at the MTJ. Forty-eight hours after injury, isometric torque deficit(injured/sham) was measured. Two groups of animals (N= 6 in each group) were tested with the only difference between the two groups being the initial tendon shortening. In Group 1 (tendon shortening = 1.2 cm,N= 6) the torque deficit was 36.7 ± 5.9% (mean ± SD). In Group 2(tendon shortening = 1.5 cm,N= 6) the torque deficit was 58.7± 7.4% (mean ± SD). No order effect was suggested by the data(P= 0.6062), but the difference in torque deficit between the two groups was highly significant (P= 0.0001). For all tests in which the tendon was temporarily shortened before muscle stimulation and stretch(N= 12) there was a visible hematoma at the MTJ similar to the injury that is common in athletic injuries. Histological evaluation 48 h after injury revealed both fiber tearing and inflammation at the MTJ. In addition, there was focal fiber damage in the muscle belly for both groups. The damage and inflammatory process, however, were more severe in the group with greater initial tendon shortening.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Respiratory sinus arrhythmia (RSA) was examined in aerobically trained (AT) and untrained (NT) college-aged males during 12 periods consisting of a 3-min sitting baseline, six common 3-min absolute exercise stages, and five 3-min recovery stages that followed voluntary exhaustion to determine the relationship of work and training status to parasympathetic influence upon the heart. RSA systematically decreased during absolute exercise, was observed at heart rates (HR) above 100 beats·min-1, and progressively increased during recovery. Additionally, independent of work stages, comparative regression analyses were conducted for both the exercise and recovery phases, separately, in which HR was regressed on RSA, as well as RSA on%˙VO2max, to contrast the obtained relationship for the AT and NT. No differences were revealed as a function of endurance training status as the slopes and intercepts obtained for the two groups from each of these analyses were similar. The within-subject correlations between RSA and%˙VO2max, calculated for each of the individuals across all 12 periods, were consistently negative. Between-subjects correlations of RSA with RR and tidal volume were predominantly nonsignificant, indicating that RSA, as measured here, is independent of individual differences in ventilatory activity and, as such, can be compared between groups during exercise. The findings demonstrate that RSA is detectable during both exercise and recovery, even at HR beyond 100 beats·min-1, and reveals a similar relationship to HR and metabolic state in both aerobically trained and untrained populations.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Studies using spectral analysis of cardiovascular variability as a noninvasive means for assessing autonomic nervous system activity have provided controversial results in athletes. One reason is that a slow breathing rate-a common feature in athletes-affects spectral estimation because it causes the low-frequency (LF) and high-frequency (HF) components to overlap. Low-frequency power increases during sympathetic activation; high-frequency corresponds to respiratory sinus arrhythmia. In this study, to assess how controlled respiration influences autonomic nervous system activity, we determined the effect of controlled and uncontrolled breathing conditions on cardiovascular variability. Our aim was to identify a standard respiratory rate for spectral estimation of cardiovascular neural control in athletes. During electrocardiographic recordings, subjects lay supine and breathed at their spontaneous frequency and at rates of 15, 12, and 10 to 14(random) breaths·min-1. Uncontrolled and random breathing rates significantly altered spectral sympathetic indices; conversely, 15 and 12 breaths·min-1redistributed respiratory related power through the HF, thus yielding correct LF power estimation. None of the breathing conditions significantly changed mean heart rate, arterial blood pressure, or spectral total power of cardiovascular variability. In conclusion, when power spectral analysis is used for assessing autonomic activity in athletes, respiration should be standardized at 15 breaths·min-1. Controlled respiration at this rate leaves autonomic nervous system activity unchanged.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Objective:Exercise enhances the dilation of the epicardial coronary arteries by vasodilator drugs and blood flow. Our goal was to determine whether coronary artery elastic properties were affected by brief exercise training.Methods:Arterial pressure and left circumflex coronary artery diameter were measured in dogs. Venous bolus injections of acetylcholine 5μg·kg-1(ACH) and nitroglycerin 25 μg·kg-1(NTG) or infusions of adenosine 0.5 μM/kg/min (ADO) were given. Fifteen-second coronary artery occlusions were performed. Dogs exercised 2 h·d-1for 7 d at 10.9 km·h-1. Experiments were repeated. Pressure and coronary radius data were used to calculate vessel wall stress and incremental wall modulus, Einc.Results:Baseline Eincand radius were not changed by exercise. Before exercise Eincincreased similarly from baseline for all vasodilators. After exercise, the increase in Eincwith ADO was unchanged. However, the increase was attenuated during ACH, abolished with occlusion, and reversed with NTG despite enhanced dilation.Conclusion:Data suggest that functional remodeling of epicardial arteries begins soon after starting exercise training, before changes in resting vessel diameter, is mediated by cGMP, and contributes to increased vascular dilation. Brief exercise training enhances the vasodilating capability and elastic properties of large coronary arteries.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

The aim of the present study was to investigate the influence of parasympathetic receptor blockade on the heart rate performance curve (HRPC). Twenty healthy male subjects performed a first cycle ergometer test (F), showing a HRPC deflection of varying degree and direction. Subjects then in random order performed two additional cycle ergometer tests, one with atropine(A) and the other with placebo (P). Two lactate turn points (LTP1, and LTP2) were determined by means of linear regression turn point analysis. The degree and direction of the deflection of the HRPC was calculated mathematically as factor kHR(kHR>0 = downsloping of HPRC; kHR<0 = upsloping of HRPC). In comparison with that in F and P, HR in A was significantly higher at rest, LTP1, LTP2, and during recovery, but not at Powermax. An upsloping deflection of the HRPC was seen in only five cases in F and P, whereas in A 10 cases were observed (P< 0.05). In A, kHRwas significantly lower than in F and P. A significant correlation for kHRwas found among F, P, and A. Independent from parasympathetic receptor blockade and the HR at Powermax, the HR at LTP2was lower in cases with negative kHR(upsloping). In A as well as in P a significant correlation was observed between kHRand HR at LTP2. The individual time course of HRPC is reproducible and may be independent of parasympathetic activity.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Purpose:Cardiovascular response of trained males (N= 20) and fit but untrained controls (N= 10) were examined during rest and passive cycle exercise (PCE).Methods:Heart rate (HR), stroke volume (SV), cardiac output (CO), total peripheral resistance (TPR), and mean arterial pressure (MAP) were measured during PCE for 6 min at intensities of 30 and 60 rpm. Also vagal influence on the heart was assessed through time series analysis of heart period variability(HPVts) at high and medium frequencies. Electromyography (EMG) was used to monitor muscle activity during PCE.Results:During PCE no differences in cardiovascular response were found between the trained and untrained groups; thus groups were combined for the remainder of the analysis. Results indicated that during light and medium PCE all subjects combined showed a significant increase in HR, CO, and MAP and a significant decrease in HPVts(P< 0.001).Conclusion:The increase in HR during passive exercise may be a result of the stimulation of mechanoreceptors. The small and similar SV response during PCE of both groups suggests that the muscle pumps may not be effective during this form of passive exercise.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

Purpose:To assess whether entrainment of breathing (E) during exercise: 1) differed according to the test protocol in well-trained triathletes, and 2) improved ventilatory efficiency during exercise.Methods:Eight triathletes performed three incremental tests until exhaustion: while cycling (CE), while running at increasing grade and constant speed (↑ GRADE) and while running at increasing speed and constant grade (↑ SPEED), respectively. E was evaluated as the percentage of breaths occurring at respiratory rates (F) corresponding to integer ratios of the exercise cycle rate. To assess whether E improved ventilatory efficiency,Δ˙VE/˙VO2between nonentrained and entrained breaths was measured at each load.Results:Mean E was higher in CE (57.2 ± 21.9%) than in ↑ GRADE (46.9± 18.7%) and ↑ SPEED (41.4 ± 17.2%). E decreased at high loads in Ce and ↑ SPEED but not in ↑ GRADE. In the group of subjects, E correlated with the degree of fitness (evaluated as˙VO2Tvent/˙VO2peak%) only during ↑ GRADE. By multiple regression analysis on all data, minute ventilation correlated with CO2production but not with the exercise cycle rate; however, eitherFor tidal volume correlated significantly with both these variables.˙VE/˙VO2was lower in entrained than nonentrained breaths at each load in CE and ↑ GRADE experiments, but the difference was small.Conclusions:In spite of some differences among protocols, triathletes showed significant E during incremental exercise tests. Spontaneous E appeared to slightly improve ventilatory efficiency during CE and ↑ GRADE protocols.

ISSN:0195-9131    

出版商:OVID    

年代:1998

数据来源: OVID