The effect of lower limb strengthening exercise on orthostatic blood pressure and the skeletal muscle pump in older people with orthostatic hypotension

Frith, J., Robinson, L., Gibbon, J.R. & Allen, J. (2023) The effect of lower limb strengthening exercise on orthostatic blood pressure and the skeletal muscle pump in older people with orthostatic hypotension. Clinical Physiology and Functional Imaging, 1–6. https://doi.org/10.1111/cpf.12866

Link to Original Article: https://onlinelibrary.wiley.com/doi/full/10.1111/cpf.12866

Key Points

- The study aimed to determine if increasing the strength of the lower limb muscles could improve the effectiveness of the venous pump and postural blood pressure in older people with orthostatic hypotension (OH).

- The intervention increased calf muscle strength by 21% but did not lead to an improvement in venous ejection fraction (EF) or orthostatic blood pressure drop.

- Visual analysis of individual case-series trends revealed increasing muscle strength with no clinically meaningful change in EF or orthostatic blood pressure.

- An 8-week lower limb strengthening exercise was not found to increase the effectiveness of the skeletal muscle pump and was not an efficacious intervention for OH.

- There was little to no venous pooling in the calf during standing in older people with OH, challenging the commonly held view on the condition.

- The study suggests that lower limb strengthening exercise does not improve the efficacy of the muscle pump and standing blood pressure in older people with orthostatic hypotension.

Introduction

The research paper discusses orthostatic hypotension (OH), a condition where there is a significant drop in blood pressure upon standing upright, affecting around 20% of community-dwelling older individuals and leading to reduced quality of life and increased mortality. Physical counter-manoeuvres (PCMs), involving voluntary contraction of skeletal muscles to increase venous return, are the first-line therapy for OH. Older people with OH are inclined to use nondrug therapies, particularly PCMs, to avoid medication, as it is one of the most tolerable therapies for this group. The paper raises the question of whether increasing the strength of these muscles would lead to improved venous function and orthostatic blood pressure, addressing the gap in knowledge regarding the potential impact of muscle strength on venous function and orthostatic blood pressure regulation.

Methods

This research paper describes an evaluative case series that aimed to assess the effects of a home-based exercise program on participants with orthostatic hypotension (OH). Participants served as their own controls and were randomized to different baseline observation periods (2, 3, or 4 weeks).

Population

The participants, who were recruited from a Falls and Syncope clinic in England, were aged 60 years or older and fulfilled international diagnostic criteria for OH. Exclusion criteria included lower limb ulceration or deep vein thrombosis, participation in physical therapy in the preceding 8 weeks, and acute illness.

Intervention

The 8-week home-based exercise program focused on progressive lower limb muscle strength using resistance bands. Each program consisted of 40 minute exercise sessions 3 to 4 times per week. The exercises were taught by a research assistant.

Outcome

The primary outcome measure was the change in orthostatic systolic blood pressure (SBP) drop, and secondary outcomes included venous ejection fraction (EF), volume (EV), calf muscle strength, lower limb strength and function, as well as symptoms, adherence, acceptability, and safety.

Data Collection

The data on postural BP and muscle strength were collected at baseline and during weekly home visits. Participants also attended a physiology laboratory at baseline, midpoint, end of intervention, and 4 weeks post intervention to assess the venous measurements.

• Home Assessments

The postural BP was recorded after 10 minutes of rest in supine position, immediately upon standing, and after 1, 2, and 3 minutes after standing. GE Carescape V100 Vital Signs Monitor was used to assess brachial artery BP. The Orthostatic Hypotension Questionnaire (OHQ) was used to assess symptoms of OH, and exercise diaries were reviewed for adherence and safety. The researchers used a dynamometer to assess Isometric Calf Muscle Strength (ICMS) by positioning participants in a seated position with hip in flexion and knee in maximal extension with the dynamometer fixed in place against a wall. The participants were asked to plantarflex the ankle against the dynamometer and only the left leg was used for each participant. The participants had three trials and the best attempt was recorded. In addition, 5x Sit to Stand (5STS) was used to assess lower limb muscle strength and function.

• Vascular Physiology Studies

The EV, EF, and VFI of the calf was measured using air plethysmography (APG). The participants rested in supine position for 10 minutes with an APG cuff inflated lightly around the calf of the test leg with the test leg raised above the heart. Once the APG volume reached its peak, the participants performed three ankle plantarflexion/dorsiflexion movements with each movement separated by 1 minute. Both legs were studied, starting with the right leg for all participants.

The researcher determined >60% as good, 40% to 60% as borderline, and <40% as poor for EF values.

Data Analysis

The study aimed to have 10 participants complete the study, taking into account a projected dropout rate of 30%. To achieve this, a total of 15 participants were recruited. In this case series design, repeated measures were plotted on time-series graphs to identify meaningful changes in a clinical context. The more observations available, the stronger the statistical power. This design is particularly valuable in assessing the initial effectiveness of interventions, especially those with a behavioral element. Although the focus is on identifying clinically significant signals rather than solely statistical significance, to avoid biases, statistical analyses are also presented alongside visual analyses.
The data were summarized using the median along with the inter‐quartile range. To compare changes in outcomes between the baseline and Week 8 (end of intervention), a one‐sample Wilcoxon's test was conducted with the significance level set at less than 0.05. For the calculation of EV and EF, the maximum volume change with tiptoe was compared to the venous volume level from standing, as opposed to the supine level. The VFI was determined by measuring the rate of change of venous filling on standing in mL/s. The average of left and right values was computed for each measure. Any EF and EV values that fell outside the normal range due to interference were excluded from the analysis.

Results

This study recruited 14 participants between September 2018 and September 2019, with four withdrawing from the study. One participant missed a key assessment and was excluded from statistical analysis but included in visual analysis for blood pressure (BP) and strength. The baseline characteristics of the participants revealed no changes in medications during the study period, and all were community-dwelling.

Primary Outcome

The systolic blood pressure (SBP) drop over the baseline, intervention, and follow-up period showed varying trends among the participants. Visual analysis illustrated wide variations in SBP drop, even during the baseline period. The median SBP drop at the baseline was 54 (32-75) mmHg, and at the end of the intervention, it was 50 (26-55) mmHg, which was not statistically different from baseline.

Secondary Outcomes

The study showed median baseline EF at 64%, and the change at the end of intervention was -6%. 4 participants were classified as borderline/poor EF values at the baseline, but the number of participants classified as borderline/poor EF values decreased to 2 with intervention. The median EV at baseline was 44 ml and 47 at the end of intervention, which equates to +9% change from baseline. The median VFI at baseline was 1.5 ml and 1.4 ml at the end of intervention, which signifies -6% change from baseline.

The median OHQ score was 2 at the baseline and 1 at the end of intervention, which was not statistically significant.

The participants demonstrated +21% change in calf strength from the baseline to the end of intervention. However, 5STS time only decreased by 4.2% from the baseline to the end of intervention.

No adverse events were reported, and the participants adhered to the exercise program adequately.

Discussion

The discussion section of this case series analysis highlights that while the exercise intervention led to increased lower limb muscle strength, it did not result in improvements in venous EF, orthostatic blood pressure (BP) drop, or symptoms. The paper discusses the theoretical benefit of lower limb muscle strengthening for orthostatic hypotension (OH) in older individuals based on previous studies. It also suggests that the multifactorial nature of the condition, including complex physiological mechanisms involved in postural BP control and the potential influence of venous pooling in the pelvis and thighs, may limit the impact of interventions focused solely on muscle strength. The study's findings challenge the common assumption of significant venous pooling in the lower limbs among those with OH, with observed venous reflux levels within normal limits. The authors also note that the small volume of blood ejected from the calf muscle and the low levels of venous reflux make it unlikely that below-knee compression garments will be effective in treating OH. Overall, the study suggests that while exercise interventions may increase muscle strength, they may not directly translate to improvements in venous EF or orthostatic BP in older individuals with OH.

Limitations

The research paper is an early phase, single case series design with a low number of participants, limiting the generalizability of the findings. However, the high number of repeated observations for each participant increases the intra-participant power. The study participants had relatively low symptom severity, possibly due to their existing treatment, leading to potential volunteer bias and limiting the generalizability of the results to those with more severe symptoms. While the intervention did lead to increased muscle strength, the short duration of the intervention raises the possibility that a longer intervention could have further increased strength and potentially improved venous EF. Therefore, the findings of this study should be interpreted cautiously due to the small sample size, potential volunteer bias, and limitations in the intervention duration.

Conclusions

In the calf area of older individuals with OH, the occurrence of excess venous pooling is minimal to negligible. It has been observed that incorporating lower limb strengthening exercises does not yield improvements in the effectiveness of the muscle pump or standing blood pressure among older individuals with OH.