Sex differences in pulmonary function during exercise

Structural and hormonal sex differences are known to exist that may influence the pulmonary system's response to exercise. Specifically, women tend to show reduced lung size, decreased maximal expiratory flow rates, reduced airway diameter, and a smaller diffusion surface than age- and height-matched men. Additionally, ovarian hormones, namely progesterone and estrogen, are known to modify and influence the pulmonary system. These differences may have an effect on airway responsiveness, ventilation, respiratory muscle work, and pulmonary gas exchange during exercise. Recent evidence suggests that during exercise, women demonstrate greater airway hyperresponsiveness and expiratory flow limitation, increased work of breathing, and, perhaps, greater exercise-induced arterial hypoxemia compared with men. The consequence of these pulmonary effects may influence exercise capacity.     

不同运动强度下恢复期心率推测运动心率的探讨

目的：研究不同运动强度下恢复期心率随恢复时间的变化特征,探讨恢复期心率与运动心率的关系,建立恢复期心率推测运动心率的方法。方法以60名男兵为对象,在功率自行车上进行不同强度（20、40、60、80、100、120、140、160、180 W）的运动,每一运动强度持续6 min;受试者佩戴心率带,实时监测运动中及恢复期的心率。结果（1）运动心率与恢复期10,20,30,40,50,60 s的心率均存在显著性差异（P＜0．05）;（2）不同运动强度恢复期心率下降值的比较,20,40和60 W强度,80、100和120 W强度以及140、160和180 W强度3段各自比较均无显著差异;上述3段强度间相应恢复心率下降值比较有显著差异（P＜0．05）;（3）相同运动强度下不同时间（10、20和30 s）的单位时间恢复期心率下降值比较,0～10 s与10～20 s和20～30 s有显著差异（P＜0．05）,10～20 s和20～30 s无显著差异;（4）针对20～60 W、80～120 W、140～180 W 3段运动强度的运动心率和恢复期10～30 s时的恢复心率,回归分析得到运动心率与恢复期心率和恢复时间的回归方程。结论不同运动强度的恢复期心率随时间的变化规律存在异同;可依不同强度的运动心率推测方程,由恢复期心率和时间推测运动心率;恢复期心率和恢复时间的最佳测量时间是运动结束后10～30 s。     

Oral magnesium therapy, exercise heart rate, exercise tolerance, and myocardial function in coronary artery disease patients

Background

Previous studies have demonstrated that in patients with coronary artery disease (CAD) upward deflection of the heart rate (HR) performance curve can be observed and that this upward deflection and the degree of the deflection are correlated with a diminished stress dependent left ventricular function. Magnesium supplementation improves endothelial function, exercise tolerance, and exercise induced chest pain in patients with CAD.

Purpose

We studied the effects of oral magnesium therapy on exercise dependent HR as related to exercise tolerance and resting myocardial function in patients with CAD.

Methods

In a double blind controlled trial, 53 male patients with stable CAD were randomised to either oral magnesium 15 mmol twice daily (n = 28, age 61±9 years, height 171±7 cm, body weight 79±10 kg, previous myocardial infarction, n = 7) or placebo (n = 25, age 58±10 years, height 172±6 cm, body weight 79±10 kg, previous myocardial infarction, n = 6) for 6 months. Maximal oxygen uptake (VO_2max), the degree and direction of the deflection of the HR performance curve described as factor k<0 (upward deflection), and the left ventricular ejection fraction (LVEF) were the outcomes measured.

Results

Magnesium therapy for 6 months significantly increased intracellular magnesium levels (32.7±2.5 v 35.6±2.1 mEq/l, p<0.001) compared to placebo (33.1±3.1.9 v 33.8±2.0 mEq/l, NS), VO_2max (28.3±6.2 v 30.6±7.1 ml/kg/min, p<0.001; 29.3±5.4 v 29.6±5.2 ml/kg/min, NS), factor k (−0.298±0.242 v −0.208±0.260, p<0.05; −0.269±0.336 v −0.272±0.335, NS), and LVEF (58±11 v 67±10%, p<0.001; 55±11 v 54±12%, NS).

Conclusion

The present study supports the intake of oral magnesium and its favourable effects on exercise tolerance and left ventricular function during rest and exercise in stable CAD patients.     

Sex differences in cardiovascular demands of refereeing during international basketball competition

Objectives: The aim of this study was to investigate the impact of sex on cardiovascular responses of referees during elite international basketball competition.

Methods: Twenty-seven elite referees (9 female; 18 male) officiated a random sample of 18 matches during the final round of the 2013 Women’s Eurobasket Championship. Continuous recordings of referees’ heart rate (HR) during matches were obtained and analyzed for average HR, relative exercise intensity (% maximum HR, HR_max) and proportion of time spent within different exercise-intensity categories.

Results: During the championship, the average match HR was >150 bpm and approximated an exercise intensity of >85% HR_max for referees. Female referees exhibited lower average match HR (156.8 ± 10.2 vs. 163.6 ± 11.6 bpm, p<0.05) and exercise intensity (86.2 ± 5.5 vs. 89.5 ± 6.0% HR_max, p<0.05) compared to male referees. Referees spent most (>70%) of each match at a HR intensity of 70-89% HR_max with females experiencing more match time within the 55-69% HR_max category compared to males. Average HR and exercise intensity was greatest for all referees during the early part of the match (Quarter 1) that declined over the match.

Conclusion: This study has demonstrated that sex significantly influences cardiovascular responses for elite basketball referees with lower responses for females potentially reflective of different movement patterns. Reductions in cardiovascular response noted during matches for all referees may reflect alterations in metabolism, match activities or induction of fatigue that should be considered in the development and training of elite referees for optimal match performance.     

Sex difference in fluid balance responses during prolonged exercise

Maintaining a proper fluid balance is important during exercise as athletes are prone to develop dehydration during exercise. Although several factors may regulate the fluid balance, little is known about the role of sex during prolonged moderate‐intensity exercise. Therefore, we compared body mass changes and fluid balance parameters in men vs women in a large heterogeneous group of participants during prolonged exercise. Ninety‐eight volunteers walked 30–50 km at a self‐selected pace. Exercise duration (8 h, 32 min) and intensity (69% HR_max) were comparable between groups. Men demonstrated a significantly larger change in body mass than women (?1.6% vs ?0.9%, respectively, P < 0.001) and a higher incidence of dehydration (defined as ≥2% body mass loss) compared with women (34% vs 12%, respectively, odds ratio = 4.2, 95% CI = 1.1–16.7). Changes in blood sodium levels were significantly different between men (+1.5 mmol/L) and women (?0.4 mmol/L), while 27% of the men vs 0% of the women showed postexercise hypernatremia (sodium levels ≥ 145 mmol/L). Moreover, men demonstrated a significantly lower fluid intake (2.9 mL/kg/h) and higher fluid loss (5.0 mL/kg/h) compared with women (3.7 and 4.8 mL/kg/h, respectively). Taken together, our data suggest that men and women demonstrate different changes in fluid balance in response to a similar bout of exercise.     

The use of heart rate variability measures to assess autonomic control during exercise

Heart rate variability (HRV) is a non-invasive indicator of cardiac autonomic modulation at rest. During rhythmic exercise, global HRV decreases as a function of exercise intensity. Measures reflecting sympathovagal interactions at rest do not behave as expected during exercise. This makes interpretation of HRV measures difficult, especially at higher exercise intensities. This problem is further confounded by the occurrence of non-neural oscillations in the high-frequency band due to increased respiratory effort. Alternative data treatments, such as coarse graining spectral analysis (CGSA), have demonstrated expected changes in autonomic function during exercise with some success. The separation of harmonic from fractal and/or chaotic components of HRV and study of the latter during exercise have provided further insight into cardioregulatory control. However, more research is needed. Some cross-sectional differences between HRV in athletes and controls during exercise are evident and data suggest longitudinal changes may be possible. Standard spectral HRV analysis should not be applied to exercise conditions. The use of CGSA and non-linear analyses show much promise in this area. Until further validation of these measures is carried out and clarification of the physiological meaning of such measures occurs, HRV data regarding altered autonomic control during exercise should be treated with caution.     

Effect of acute exercise-induced fatigue on maximal rate of heart rate increase during submaximal cycling

Different mathematical models were used to evaluate if the maximal rate of heart rate (HR) increase (rHRI) was related to reductions in exercise performance resulting from acute fatigue. Fourteen triathletes completed testing before and after a 2-h run. rHRI was assessed during 5 min of 100-W cycling and a sigmoidal (rHRI_sig) and exponential (rHRI_exp) model were applied. Exercise performance was assessed using a 5-min cycling time-trial. The run elicited reductions in time-trial performance (1.34 ± 0.19 to 1.25 ± 0.18 kJ · kg^?1, P < 0.001), rHRI_sig (2.25 ± 1.0 to 1.14 ± 0.7 beats · min^?1 · s^?1, P < 0.001) and rHRI_exp (3.79 ± 2.07 to 1.98 ± 1.05 beats · min^?1 · s^?1, P = 0.001), and increased pre-exercise HR (73.0 ± 8.4 to 90.5 ± 11.4 beats · min^?1, P < 0.001). Pre-post run difference in time-trial performance was related to difference in rHRI_sig (r = 0.58, P = 0.04 and r = 0.75, P = 0.003) but not rHRI_exp (r = ?0.04, P = 0.9 and r = 0.27, P = 0.4) when controlling for differences in pre-exercise and steady-state HR. rHRI_sig was reduced following acute exercise-induced fatigue, and correlated with difference in performance.     

新战士运动应激时心理状态与心率和血压变化的关系

 目的 观测不同心理状态武警新战士运动应激时心率和血压的反应。方法 采用精神症状自评量表(SCL-90)对新战士进行集体心理状态测试,选取总分＞160分的40名战士纳入实验组(低心理素质组),另选取总分≤160分的40名战士作为对照组(高心理素质组)。采用GE-CASE活动平板运动测试系统,按照标准的Bruce方案测定两组战士在安静时、运动应激中每3 min和恢复阶段每1 min的心率和血压。结果 实验组达到极量运动的人数少于对照组,且出现不良反应如头晕、胸闷增多。实验组基础心率高于对照组(80.0±9.8)次/min vs (69.2±9.2)次/min,差异有统计学意义(P=0.023),极量运动时舒张压异常增高(96.6±6.4) mmHg vs (78.4±8.3) mmHg,差异有统计学意义(P=0.013),并伴有心率下降。恢复阶段,实验组心率恢复较慢。结论 不同心理状态的新战士在运动应激时出现的心血管系统反应存在显著差异,低心理素质组的战士不良反应较高心理素质组的战士增多,可能与其机体内各种应激激素分泌失衡有关。
     

武警新战士运动应激时心率和血压的变化

 目的 检测新入伍战士运动应激时心率和血压的反应.方法 采用活动平板运动试验,按照标准的Bruce方案从第3级开始对85名新入伍战士进行试验,测量休息时、运动应激中每3 min和恢复阶段每2 min的心率和血压.结果 运动应激开始后心率较安静时成倍增加,此后心率随着运动应激量的增加而增快,极量心率约为安静时的2.5倍,增加117次/min,期间有两个高峰,分别为运动至第5级和第7级时.恢复期心率以停止运动后2 min内减慢明显(减慢36次/min),10 min后恢复正常;运动应激时血压升高,以收缩压升高为主,应激过程中收缩压和舒张压分别约增加21 mmHg和4 mmHg,12 min后恢复至安静时水平,运动应激后舒张压持续降低.结论 运动应激时心率和收缩压的变化呈双峰型,心率恢复较血压快.     

Physical fitness in adolescents with normal weight and overweight

We studied the associations of overweight (OW, BMI > or =85th percentile) and physical activity (PA) with physical fitness in adolescents. The nationally representative sample was 1120 boys and 1146 girls, aged 15-16 years. Height and weight were self-reported. The level of PA was based on self-reported frequency and duration of sweating during organized and non-organized activity. Fitness was measured by sit-ups, sit-and-reach, five-jump, back-and-forth jumping, ball skills, coordination and endurance shuttle run tests. The fitness index was calculated as the mean of z-scores for individual tests. The prevalence of OW was 17.3% in boys and 11.8% in girls. The main effect of PA (in analysis of variance) on all fitness tests was significant (P< or =0.005). The main effect of OW was significant (P<0.002) for all tests, except for sit-and-reach. According to linear regression models, the association between PA and fitness was stronger than that between OW and fitness. Sit-ups, endurance shuttle-run and fitness index showed the strongest association with PA (standardized beta coefficients 0.31-0.49). OW was not associated with sit-and-reach test (coefficient 0.04) and only weakly with the ball skills test (coefficients -0.10 to -0.12). In conclusion, OW had the most negative association with cardiorespiratory and muscle endurance, and explosive power tests.     

Associations of fitness and physical activity with orthostatic responses of heart rate and blood pressure at midlife

Cardiorespiratory fitness (CRF) and physical activity (PA) are associated with autonomic function, but their associations to orthostatic autonomic responses are unclear in epidemiological setting. We hypothesized that higher CRF and PA would associate with higher immediate vagal responses and lower incidence of adverse findings during orthostatic test. At age of 46, 787 men and 938 women without cardiorespiratory diseases and diabetes underwent an orthostatic test (3‐minutes sitting, 3‐minutes standing) with recording of RR intervals (RRi) and blood pressure (BP) by finger plethysmography. Acute responses of RRi (30:15 ratio) and BP were calculated. CRF was measured by a submaximal step test and daily amount of moderate‐to‐vigorous PA (MVPA) for 2 weeks by wrist‐worn accelerometer. Lifelong PA was based on questionnaires at ages of 14, 31, and 46. High CRF was significantly associated with higher RRi 30:15 ratio (adjusted standardized β = 0.17, P < 0.001) and milder acute decrease of systolic BP while standing (β = 0.10, P = 0.001), while MVPA was not (β = 0.04 for RRi 30:15 ratio and β = 0.05 for systolic BP acute response). High lifelong PA was significantly associated with higher RRi 30:15 ratio (β = 0.08, P = 0.002) but not with acute systolic BP response. Those in the lowest tertile of CRF had 9.2‐fold risk (P = 0.002) of having postural orthostatic tachycardia syndrome compared to more fit. Cardiorespiratory fitness and lifelong physical activity, but not current physical activity, were independently associated with higher cardiac vagal response to orthostasis. The present results underscore the importance fitness and lifelong physical activity in prevention of abnormal autonomic function and related cardiovascular risk.     

Effects of antiarrhythmic agents on left ventricular function during exercise in patients with chronic left ventricular dysfunction

This study was designed to determine the effects of antiarrhythmic agents on global left ventricular (LV) function during exercise in patients with chronic LV dysfunction. Thirty-five patients with LV dysfunction [LV ejection fraction (LVEF) < 45%] and ventricular arrhythmias were studied. They were randomly classified into 3 groups: patients who received a single oral dose of 6 mg/kg disopyramide phosphate (n = 12), those who received a single oral dose of 4 mg/kg mexiletine hydrochloride (n = 12), and those who received a single oral dose of 4 mg/kg pilsicainide hydrochloride (n = 11). First, all patients were subjected to baseline rest and peak exercise, equilibrium-gated cardiac-pool scintigraphy with 99mTc-human serous albumin of 740 MBq (baseline data). Second, on a separate day, they were given drugs once, and were subsequently subjected to rest and peak exercise equilibrium-gated cardiac-pool scintigraphy. Exercise LVEF and peak ejection rate (PER) after administration were significantly lower in the disopyramide and pilsicainide groups than in the mexiletine group (p < 0.05, respectively). The changes in LVEF and PER from rest to peak exercise after administration were significantly less than the baseline changes in those in the disopyramide and pilsicainide groups (p < 0.05, respectively). However, no significant changes in functional parameters were recognized in the mexiletine group. Due care should be taken when disopyramide and pilsicainide are administered to patients with chronic LV dysfunction since they reduce systolic LV function during exercise.     

Interaction of cardiac and muscle mechanical afferents on baroreflex control of the sinus node during dynamic exercise

The effects of cardiopulmonary baroreceptors and muscle mechanoreceptors stimulation on cardiac baroreflex sensitivity (BRS), and heart rate variability (HRV) were evaluated by measuring continuously and non‐invasively systolic blood pressure (SBP) and pulse interval (PI) during upright and supine passive cycling. BRS and HRV were evaluated with the cross‐correlation method (xBRS) and in the frequency domain, respectively. At rest, the shift from upright to supine posture enhanced xBRS from 16.4±12.1 to 23.4±12.9 ms/mmHg, and the high frequency (HF, 0.15–0.4 Hz) power of HRV from 48.9±18.6 to 55.1±14.7 normalized units (NU), while it attenuated the low‐frequency (LF, 0.04–0.15 Hz) power from 51.1±18.6 to 44.9±14.7 NU (P<0.05), respectively. During both upright and supine passive exercise, xBRS and the HF power were attenuated (10.0±8.0 and 12.5±9.0 ms/mmHg; 41.1±21.2 and 41.5±12.7 NU, respectively; P<0.05) and the LF power increased (58.8±21.2 and 58.5±12.7 NU, P<0.05), compared with rest. The effect of mechanoreflex activation overrides that of the cardiopulmonary baroreceptors loading resulting in decreased cardiac vagal outflow and reduced BRS during supine passive exercise.     

曲美他嗪对慢性心力衰竭患者心功能及心率变异性的影响

目的探讨曲美他嗪对慢性心力衰竭（CHF）患者心功能及心率变异性（HRV）的影响。方法将60例CHF患者随机分为治疗组和对照组,每组30例,对照组给予常规治疗,治疗组在常规治疗的基础上加用曲美他嗪治疗6个月,观察两组患者治疗前后NYHA分级、左心室舒张末期内径（LVEDd）、左心室射血分数（LVEF）、N末端原脑利钠肽（NT-pro-BNP）及6min步行距离（6-MWD）的变化,采用12导联同步1-IOLTER检测系统检查,测定HRV时域指标（SDNN、SDANNindex MSDD、PNN50）。结果6个月后,治疗组患者的心功能明显改善,LVEDd及NT—pro—BNP与对照组相比明显降低,LVEF及6-MWD与对照组相比明显增加,HRV参数明显好转。结论曲美他嗪可以改善CHF患者的心功能及HRV。     

Rate of reduction of heart rate variability during exercise as an index of physical work capacity

Breathing rates during physical exercise suggest that, during these conditions, the high-frequency (HF) bandwidth of heart rate variability (HRV) analysis should be extended beyond conventional guidelines. However, there has been little investigation of the most appropriate choice of HF bandwidth during exercise. HRV analysis was performed in 10 males and six females during progressive bicycle exercise. Cardiac cycle (RR) interval and breath-by-breath respiratory data were simultaneously recorded. HRV powers were determined for the band-limited ranges 0.04-0.15 Hz [low-frequency (LF)], 0.15-0.4 Hz (HF 0.4) and 0.15-bf Hz (HF bf, where bf represents maximum breathing frequency). Mono-exponential functions described the relationship between HRV and work rate for each bandwidth (r=0.92-0.95) and were used to calculate the "HRV decay constant" (work rate associated with a 50% reduction in HRV power). The HRV decay constants for each bandwidth were linearly related to maximal work rate (r>0.71; P<0.001) and were substantially greater in males than in females (P<0.001). There was a significant difference between the HRV decay constants for HF 0.4 and HF bf (P<0.005) in both genders. The HRV decay constants for the LF and HF bf bandwidths appear to provide an indication of work capacity from submaximal exercise, without prior assumption regarding heart rate and its relationship with work rate.     

Exercise testing in children and adolescents with chronic fatigue syndrome

The objective of this study was to evaluate exercise capacity in children and adolescents diagnosed with Chronic Fatigue Syndrome (CFS). We examined 20 patients (12 girls and 8 boys; mean age 14.9 +/- 3.7 years) diagnosed with CFS. Exercise capacity was measured using a maximal exercise test on a bicycle ergometer and an expired gas analysis system. Fatigue was assessed using a questionnaire and a daily activity diary was used to describe activities for three days. Z-scores were calculated using age- and sex-matched reference values. Z-scores in children and adolescents with CFS were - 0.33 +/- 1.0 (p = 0.17) for peak oxygen uptake, - 1.13 +/- 1.41 (p = 0.002) for relative peak oxygen uptake [ml/kg/min] and - 0.93 +/- 1.29 (p = 0.07) for maximal work load. Both heart rate and blood pressure at peak performance were significantly reduced compared to reference values. Fatigue levels were significantly positively associated with age and negatively with blood pressure at peak exercise (p < 0.05). In conclusion maximum exercise testing was feasible in young people with CFS. Maximal exercise capacity was only reduced in a minority of the patients and was related to current physical activity levels.     

准备运动与放松运动对剧烈运动中及运动后颈总动脉血流速度的影响

８名男性大学生参加了下列３组实验：（１）单纯５分钟的剧烈运动（大于９０％ｏｆＶＯ２ｍａｘ）;（２）５分钟的准备运动（５０％ｏｆＶＯ２ｍａｘ）后再进行上述剧烈运动;（３）上述剧烈运动后再进行５分钟的放松运动（５５％ｏｆＶＯ２ｍａｘ）。在上述实验的同时,检测了每位被试者的颈总动脉血流平均速度（平均ＶＣＣＡ）、心率（ｆｃ）、左肱动脉平均血压（Ｐｍ）,并根据血流速度参数计算出反映脑血流阻力的指标———阻抗指数（ＲＩ）。结果显示：在５分钟的剧烈运动中,不论有否准备运动,上述４种参数均明显增加。在准备运动中,平均ＶＣＣＡ和ｆｃ均有所增加,ＲＩ的增加几乎达到了剧烈运动时的水平。剧烈运动后,Ｐｍ和ｆｃ很快恢复,放松运动中这两个指标有所恢复。但是平均ＶＣＣＡ和ＲＩ在放松运动中保持着剧烈运动时的高水平。准备运动中阻抗指数明显增加提示脑血流阻力增加,这可防止由于颈总动脉平均血流速度和心率的增加而引起脑血流的过多增加（尤其是对那些有脑血管缺陷的人）,有利于机体接着进行剧烈的运动。本研究中的放松运动可减缓颈总动脉血流平均速度等几种生理指标在剧烈运动后的恢复速度,使剧烈运动后机体（尤其是心脑血管调节功能差的人）的生理功能逐渐得到恢复,?     

血尿酸检测在慢性心衰患者临床症状评估上的应用

目的探讨血尿酸在慢性心力衰竭（CHF）患者体内的分布水平,以及与临床症状严重程度的关系。方法将我院393例CHF患者按随机数字表法选择出CHF患者69例,进而按照NYHA分级标准,分为心功能Ⅰ～Ⅱ级组23例,心功能Ⅲ级组26例,心功能Ⅳ级组20例,同时选取25例无任何疾患的健康体检者为对照组。采用全自动生化分析仪,对健康对照者和慢性心衰患者进行血尿酸含量测定,并与左室射血分数（LVEF）以及二尖瓣瓣尖水平的E峰和A峰最大速度比（E／A）进行相关性分析。结果健康对照组血尿酸含量为（239．72±102．31）μmol／L,CHF患者心功能I～Ⅱ级组血尿酸含量为（323．65±108．36）μmol／L,心功能Ⅲ级组血尿酸含量为（393．61±116．37）μmot／L,心功能Ⅳ级组血尿酸含量为（435．53±98．37）μmol／L,各组间血尿酸含量差异有显著统计学意义（P〈0．01）,随心衰程度的加重,血尿酸水平也显著地增加。相关性分析发现心衰患者血尿酸水平与LVEF呈显著负相关（r=-0．53,P〈0．01）,与E／A也呈显著负相关（r=-0．38,P〈0．01）。结论CHF患者血清尿酸水平与心功能分级存在相关关系,可以作为评价CHF患者心功能损害程度以及临床转归的一项监测指标。