Blood pressure responses to acute static and dynamic exercise in three racial groups

Acute beetroot juice reduces blood pressure in young Black and White males but not females

A complex interplay of social, lifestyle, and physiological factors contribute to Black Americans having the highest blood pressure (BP) in America. One potential contributor to Black adult's higher BP may be reduced nitric oxide (NO) bioavailability. Therefore, we sought to determine whether augmenting NO bioavailability with acute beetroot juice (BRJ) supplementation would reduce resting BP and cardiovascular reactivity in Black and White adults, but to a greater extent in Black adults. A total of 18 Black and 20 White (∼equal split by biological sex) young adults completed this randomized, placebo-controlled (nitrate (NO3-)-depleted BRJ), crossover design study. We measured heart rate, brachial and central BP, and arterial stiffness (via pulse wave velocity) at rest, during handgrip exercise, and during post-exercise circulatory occlusion. Compared with White adults, Black adults exhibited higher pre-supplementation resting brachial and central BP (Ps ≤0.035; e.g., brachial systolic BP: 116(11) vs. 121(7) mmHg, P = 0.023). Compared with placebo, BRJ (∼12.8 mmol NO3-) reduced resting brachial systolic BP similarly in Black (Δ-4±10 mmHg) and White (Δ-4±7 mmHg) adults (P = 0.029). However, BRJ supplementation reduced BP in males (Ps ≤ 0.020) but not females (Ps ≥ 0.299). Irrespective of race or sex, increases in plasma NO3- were associated with reduced brachial systolic BP (ρ = -0.237, P = 0.042). No other treatment effects were observed for BP or arterial stiffness at rest or during physical stress (i.e., reactivity); Ps ≥ 0.075. Despite young Black adults having higher resting BP, acute BRJ supplementation reduced systolic BP in young Black and White adults by a similar magnitude, an effect that was driven by males.

Wave reflection and central aortic pressure are increased in response to static and dynamic muscle contraction at comparable workloads

We determined the effects of static and dynamic muscle contraction at equivalent workloads on central aortic pressure and wave reflection. At random, 14 healthy men and women (23 +/- 5 yr of age) performed a static handgrip forearm contraction [90 s at 30% of maximal voluntary contraction (MVC)], dynamic handgrip contractions (1 contraction/s for 180 s at 30% MVC), and a control trial. During static and dynamic trials, tension-time index was controlled by holding peak tension constant. Measurements of brachial artery blood pressure and the synthesis of a central aortic pressure waveform (by radial artery applanation tonometry and generalized transfer function) were conducted at baseline, during each trial, and during 1 min of postexercise ischemia (PEI). Aortic augmentation index (AI), an index of wave reflection, was calculated from the aortic pressure waveform. AI increased during both static and dynamic trials (static, 5.2 +/- 3.1 to 11.8 +/- 3.4%; dynamic, 5.8 +/- 3.0 to 13.3 +/- 3.4%; P < 0.05) and further increased during PEI (static, 18.5 +/- 3.1%; dynamic, 18.6 +/- 2.9%; P < 0.05). Peripheral and central systolic and diastolic pressures increased (P < 0.05) during both static and dynamic trials and remained elevated during PEI. AI and pressure responses did not differ between static and dynamic trials. Peripheral and central pressures increased similarly during static and dynamic contraction; however, the rise in central systolic pressure during both conditions was augmented by increased wave reflection. The present data suggest that wave reflection is an important determinant of the central blood pressure response during forearm muscle contractions.

Normal exercise blood pressure response in African-American women with parental history of hypertension

BACKGROUND

Genetic and environmental hypotheses may explain why normotensive persons at high risk of developing hypertension often exhibit greater cardiovascular reactivity to stressors than those at low risk.

METHODS

Pearson's correlation was used to evaluate reproducibility and independent t test to compare the cardiovascular responses to 30 W of exercise of normotensive young adult African-American women with positive and negative parental histories (PH) of hypertension (PH, n = 23; PH, n = 20).

RESULTS

Correlations were significant for duplicate measurements. The effects of PH on blood pressure measured at rest and during exercise were not statistically significant (P > 0.1). A nearly significant trend for greater resting (.-)VO(2) (P = 0.08) was detected in the PH than in the PH group (3.67 +/- 0.18 versus 3.26 +/- 0.14 mL/kg/min).

CONCLUSION

A hyper-reactive blood pressure response to exercise, characteristic of the evolution of hypertension, may not be present among the normotensive female offspring of hypertensive African Americans. The significance of an 11% intergroup difference in the mean resting (.-)VO(2) observed in this study is unclear.

Pressor Response to Static and Dynamic Knee Extensions at Equivalent Workload in Humans

Static exercise has been thought to induce greater pressor response than dynamic exercise, but in contrast it has been recently reported that repetitive muscle contraction recruiting small muscles evokes greater response than sustained contraction. It remained unknown whether sustained contraction induces greater pressor response if large muscles were recruited. Nine subjects performed three types of isometric knee extensions recruiting the large muscle group, i.e., 2-min sustained (20% and 40% maximal voluntary contraction [MVC]) and 4-min repetitive (40% MVC, duty cycle = 1:1 s) muscle contractions. Compared under the equivalent TTI and exercising duration (2 min), the changes in femoral arterial blood flow and VO(2) from baseline (Delta BF, Delta VO(2)) were significantly less during sustained contraction than during repetitive contraction (sustained vs. repetitive; Delta BF: +92 +/- 195 vs. +1,174 +/- 269 ml.min(-1), Delta VO(2): +53 +/- 12 vs. +180 +/- 32 ml.min(-1), mean +/- SE, p < 0.05), although the change in mean arterial pressure (Delta MAP) was greater during sustained contraction (+24 +/- 3 vs. +19 +/- 3 mmHg). Compared under the equivalent TTI and peak tension (40% MVC), Delta BF and Delta VO(2) were less and Delta MAP was greater during sustained contraction (Delta BF: -296 +/- 176 vs. +868 +/- 272 ml.min(-1); Delta VO(2): +104 +/- 16 vs. + 212 +/- 46 ml.min(-1); Delta MAP: +37 +/- 8 vs. +20 +/- 4 mmHg). Moreover Delta MAP during postexercise occlusion of the active limb was significantly greater after sustained contraction than after repetitive contraction (+17.0 +/- 2.8 vs. +9.5 +/- 4.4 mmHg). These results demonstrated that pressor response is greater during sustained than during repetitive contraction, recruiting a large muscle group. This finding should be mainly due to the greater accumulation of metabolites in active muscles during sustained contraction.

Considerações sobre a medida da pressão arterial em exercícios contra-resistência

A pressão arterial (PA) é uma variável cuja quantificação em sessões de treinamento é desejável, já que tem relação com as demandas cardiovasculares no esforço. No caso de exercícios contra-resistência (ECR), porém, os valores obtidos estão sujeitos a erros, dependendo da técnica de medida adotada. Este texto tem por objetivo revisar os métodos de medida da PA no ECR, sugerindo formas de reduzir as discrepâncias das medidas indiretas quando comparadas com o método direto. A medida direta da PA é feita por cateterismo intra-arterial (CI). Este método é tido como padrão-ouro mas, devido a sua natureza invasiva, é um procedimento pouco usual. Além disso, sua aplicação não seria indicada em indivíduos assintomáticos, uma vez associada a riscos de dor, espasmo e oclusão arterial, síncope vasovagal e sangramento. Dentre os métodos indiretos, destacam-se o fotoplestimográfico (Finapres) e o auscultatório (MA). Poucos são os estudos comparativos entre esses procedimentos de medida durante ECR, a ênfase sendo maior em atividades aeróbias e no repouso. Dentre os estudos revisados, não foram localizados trabalhos comparando o CI com Finapres durante ECR e apenas três com o método auscultatório. Em suma, o CI parece pouco viável e ético para quantificar a PA em ECR. O Finapres é considerado o melhor procedimento indireto, mas depende de equipamento, cujo custo é elevado e a fabricação, suspensa. O MA pode subestimar o valor real da PA, em função de limitações inerentes à técnica e das características dos exercícios observados. No entanto, alguns procedimentos durante a mensuração podem reduzir essas diferenças, como realizá-la o mais tardiamente possível, antes do término do exercício. Enfim, apesar das discrepâncias referentes aos valores absolutos, as medidas obtidas pelo método auscultatório podem ser sensíveis para identificar tendências do impacto sobre a PA, decorrentes de diferentes situações de prescrição de ECR.

Cardiovascular responses to static and dynamic contraction during comparable workloads in humans

Previous studies suggest that the blood pressure response to static contraction is greater than that caused by dynamic exercise. In anesthetized cats, however, pressor responses to electrically induced static and dynamic contraction of the same muscle group are similar during equivalent workloads and peak tension development [i.e., similar tension-time index (TTI)]. To determine if the same relationship exists in humans, where contraction is voluntary and central command is present, dynamic (180 s; 1/s) and static (90 s) contractions at 30% of maximal voluntary contraction (MVC) were performed. Dynamic contraction also was repeated at the same TTI for 90 s at 60% MVC. Mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), MAP during postexercise arterial occlusion (an index of the metaboreceptor-induced activation of the exercise pressor reflex), and relative perceived exertion (RPE) (an index of central command) were assessed. No differences in these variables were found between static and dynamic contraction at a tension of 30% MVC. During dynamic contraction at 60% MVC, changes in MAP (16 +/- 3 vs. 19 +/- 4 mmHg) and absolute HR (92 +/- 6 vs. 69 +/- 5 beats/min), CO (7.9 +/- 0.4 vs. 6.3 +/- 0.3 l/min), RPE (16 +/- 1 vs. 13 +/- 1), and MAP during postexercise arterial occlusion (115 +/- 3 vs. 100 +/- 4 mmHg) were greater than during static contraction (P < 0.05). Thus increases in MAP and HR, activation of central command, and muscle metabolite-induced stimulation of the exercise pressor reflex during static and dynamic contraction in humans seem to be similar when peak tension and TTI are equal. Augmented responses to dynamic contraction at 60% MVC are likely related to greater activation of these two mechanisms.