Respiratory pump contributions in cerebrovascular and postural control responses during orthostatic stress in older women

Updates in inspiratory muscle training for older adults: A systematic review

Systematic reviews support the benefits of inspiratory muscle training (IMT) for exercise performance. Recently, many health benefits from IMT have been reported in older adults. Therefore, this work reviewed the literature focusing on IMT effects beyond physical performance in older adults, such as cardiorespiratory, metabolic, and postural balance outcomes. Searches were conducted with the following terms: ("respiratory muscle training" OR "inspiratory muscle training") OR ("inspiratory muscle strength training") AND ("elderly" OR "older" OR "aging" OR "aging"), and using the databases: MEDLINE (PubMed), SCOPUS and EUROPE PMC. Of the 356 articles found, 13 matched the inclusion criteria after screening. Based on reviewed studies, four to eight weeks of IMT (Mostly from 50 % up to 75 % of MIP, 7 days/week) improve cardiac autonomic control at rest and post-exercise, cerebrovascular response to orthostatic stress, static and dynamic balance, blood pressure control, endothelial function, and oxidative stress in older adults. The benefits of IMT in cardiac autonomic and vascular functions are reversed after training cessation. It thus appears that IMT promotes broad physiological gains for the older population. It is necessary to carry out more randomized clinical trials on the subject to confirm the findings of this research.

Heated environment increases blood pressure drop and postural sway during initial orthostasis in healthy subjects

PURPOSE

We tested the hypothesis that heat stress influences the closed-loop cardio-postural control by an increased blood pressure (BP) drop and postural sway.

METHODS

Fourteen healthy individuals (eight women) performed two orthostatic tests under thermal reference (TC; ~ 24 ºC) and HOT (~ 38 ºC) conditions. The center-of-pressure (COP) displacements and the electromyography (EMG) activity of the calf muscles (medial gastrocnemius and tibialis anterior) were recorded during the initial orthostasis (ORT onset) after the supine-to-stand challenge. At the same period, BP (beat-to-beat) was continuously monitored, and supine-to-stand variations (∆%) were calculated. Sublingual temperature (Tsl) was measured as a surrogate of internal temperature.

RESULTS

Tsl increased in HOT compared to TC (TC 36.5 ± 0.3 vs. HOT 36.7 ± 0.3 ºC; p < 0.01). COP distance was greater in HOT compared to TC condition (TC 596.6 ± 242.4 vs. HOT 680.2 ± 249.1 mm; p < 0.01). EMG activity of the gastrocnemius decreased in HOT compared to TC condition (TC 95.5 ± 19.8 vs. HOT 78.4 ± 22.8%mV; p = 0.02). EMG of tibialis did not change between TC and HOT (TC 83.5 ± 42.9 vs. HOT 66.1 ± 31.9% mV; p = 0.29). BP showed a greater fall in HOT compared to TC condition (∆%TC - 24.5 ± 13.2 vs. ∆%HOT - 33.2 ± 20.2%; p = 0.01).

CONCLUSION

Heat stress causes a greater fall in blood pressure and a reduction in musculoskeletal pump activity during orthostatic onset. These effects could be potential mechanisms that underlie augmented postural instability under a heated environment.

Respiratory training in older women: Unravelling central and peripheral hemodynamic slow oscillatory patterns

We hypothesized that inspiratory muscle training (IMT) increases the respiratory-induced low-frequency oscillations of mean blood pressure (MBP) and middle cerebral artery blood velocity (MCAv), upregulating cerebrovascular function in older women. Firstly, participants were recorded with free-breathing (FB) and then breathed at a slow-paced frequency (0.1 Hz; DB test) supported by sonorous metronome feedback. Blood pressure was recorded using finger photoplethysmography method, ECG, and respiration using a thoracic belt. To obtain the MCAv a transcranial ultrasound Doppler device was used. Spectral analysis of MBP, R-R intervals, and mean MCAv time series was obtained by an autoregressive model. The transfer function analysis (TFA) was employed to calculate the coherence, gain, and phase. After that, older women were enrolled in a randomized controlled protocol, the IMT-group (n = 8; 64 ± 3 years-old) performed IMT at 50 % of maximal inspiratory pressure (MIP), and Sham-group, a placebo training at 5 % MIP (Sham-group; n = 6; 66 ± 3 years-old). Participants breathed against an inspiratory resistance twice a day for 4-weeks. DB test is repeated post IMT and Sham interventions. IMT-group, compared to Sham-group, augmented tidal volume responses to DB (Sham-group 1.03 ± 0.41 vs. IMT-group 1.61 ± 0.56 L; p = 0.04), increased respiratory-induced MBP (Sham-group 26.37 ± 4.46 vs. IMT-group 48.21 ± 3.15 mmHg²; p = 0.04) and MCAv (Sham-group 14.16 ± 31.26 vs. IMT-group 79.90 ± 21.76 cm²s^-2; p = 0.03) slow oscillations, and reduced TFA gain (Sham-group 2.46 ± 1.32 vs. IMT-group 1.78 ± 1.30 cm·s^-1.mmHg^-1; p = 0.01). Our findings suggest that IMT increases the respiratory-induced oscillations in MBP and MCAv signals and reduces TFA gain. It seems compatible with an improved dynamic cerebrovascular regulation following IMT in older women.

Orthostatic intolerance: a handicap of aging or physical deconditioning?

Despite several studies that have been investigated physical inactivity and age-related effects on orthostatic tolerance, impaired hemodynamics and postural balance responses to orthostatic stress are incorrectly attributed to aging or sedentarism alone. The isolated effects from aging and sedentarism should be investigated through comparative studies between senior athletes and age-matched controls, and physical activity assessments on aging follow-up studies. On the other hand, bed rest and space flight studies mimic accelerated physical inactivity or disuse, which is not the same physiological decline provoked by aging alone. Thus, the elementary question is: could orthostatic intolerance be attributed to aging or physical inactivity? The main purpose of this review is to provide an overview of possible mechanisms underlying orthostatic tolerance contrasting the paradigm of aging and/or physical inactivity. The key points of this review are the following: (1) to counterpoint all relevant literature on physiological aspects of orthostatic tolerance; (2) to explore the mechanistic aspects underneath the cerebrovascular, cardiorespiratory, and postural determinants of orthostatic tolerance; and (3) examine non-pharmacological interventions with the potential to counterbalance the physical inactivity and aging effects. To date, the orthostatic intolerance cannot be attributed exclusively with aging since physical inactivity plays an important role in postural balance, neurovascular and cardiorespiratory responses to orthostatic stress. These physiological determinates should be interpreted within an integrative approach of orthostatic tolerance, that considers the interdependence between physiological systems in a closed-loop model. Based on this multisystem approach, acute and chronic countermeasures may combat aging and sedentarism effects on orthostatic tolerance.

Psychophysiological Indicators of Postural Control. Contribution of the Russian Scientific School. Part I

This article aimed to systematically review the published results of studies of psychophysiological mechanisms of posture maintenance and identify the key factors that influence the effectiveness of postural control. The recommendations of "Preferred Reporting Elements for Systematic Reviews and Meta-Analyzes" (PRISMA) were followed for the review. The results were classified, taking into account the target psychophysiological mechanisms and factors affecting postural control. The article presents the theoretical and empirical results of the Russian scientific school of research on the role of support afferentation in the sensorimotor mechanisms of cognitive and postural functions. Due to the limited number of randomized studies found, it was impossible to make meta-analytic comparisons, so the literature analysis was carried out only qualitatively. Meanwhile, our systematic review provides promising information about possible relationships between stabilometric and psychological indicators of postural control, which have theoretical significance and application in the correction and training of posture control. However, more thorough research is needed to overcome the methodological shortcomings that we have encountered in our qualitative analysis.

The interplay between heated environment and active standing test on cardiovascular autonomic control in healthy individuals

Objective.To investigate the interplay between active standing and heat stress on cardiovascular autonomic modulation in healthy individuals.Approach.Blood pressure (BP) and ECG were continuously recorded during 30 min in supine (SUP) and 6 min in orthostatic position (ORT) under thermal reference (TC; ∼24 °C) or heated environment (HOT; ∼36 °C) conditions, in a randomized order. All data collection was performed during the winter and spring seasons when typical outdoor temperatures are ∼23 °C. Spectral analysis was employed by the autoregressive model of R-R and systolic blood pressure (SBP) time series and defined, within each band, in low (LF, 0.04 to 0.15 Hz) and high (0.15-0.40 Hz) frequencies. The indices of cardiac sympathetic (LF) and cardiac parasympathetic (HF) were normalized (nu) dividing each band power by the total power subtracted the very-low component (<0.04 Hz), obtaining the cardiac autonomic balance (LF/HF) modulation. The gain of the relationship between SBP and R-R variabilities within the LF band was utilized for analysis of spontaneous baroreflex sensitivity (alpha index;αLF). Nonlinear analysis was employed through symbolic dynamics of R-R, which provided the percentage of sequences of three heart periods without changes in R-R interval (0V%; cardiac sympathetic modulation) and two significant variations (2UV% and 2LV%; cardiac vagal modulation).Main results.HOT increased 0V% and HR, and decreasedαLF and 2UV% during SUP compared to TC. During ORT, HOT provokes a greater increment on HR, LF/HF and 0V%, indexes compared to ORT under TC.Significance.At rest, heat stress influences both autonomic branches, increasing sympathetic and decreasing vagal modulation and spontaneous baroreflex sensitivity. The augmented HR during active standing under heat stress seems to be mediated by a greater increment in cardiac sympathetic modulation, showing an interplay between gravitational and thermal stimulus.

Association between Cardiac Autonomic Control and Postural Control in Patients with Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder that affects postural and cardiac autonomic control. However, since it is unknown whether these changes are associated, the objective of this study was to determine whether such a relationship exists. Twenty-three patients with PD participated. The RR intervals were recorded in different positions and heart rate variability (HRV) was analyzed. Postural sway was analyzed based on the center of pressure. No significant differences on HRV indices were induced by postural change. A correlation was found between these indices and postural control, high frequency (HF), and anterior-posterior (AP) root mean square (RMS-AP) (r = 0.422, p = 0.045), low frequency (LF)/HF, and AP mean velocity (r = 0.478, p = 0.021). A correlation was found between HRV induced by postural change and postural control, Δ LF/HF and RMS-AP (r = 0.448, p = 0.032), Δ LF/HF and ellipse area (r = 0.505, p = 0.014), Δ LF/HF and AP mean velocity (r = -0.531; p = 0.009), and Δ LF and AP mean velocity (r = -0.424, p = 0.044). There is an association between the autonomic and postural systems, such that PD patients with blunted cardiac autonomic function in both the supine and orthostatic positions have worse postural control.

Inspiratory muscles contributions to postural control in healthy older women

It was hypothesized that induced inspiratory muscles effort, by an acute inspiratory resistance load (IRL) use, increases the postural sway and the neuromuscular activity of postural muscles in older adults. Fifteen older women breathed spontaneously, controlled (15 cycles/minute), and with acute IRL (15 cycles/minute and target load of 30 % of maximal inspiratory pressure) in random order. The breathing tasks were performed in an orthostatic position (eyes closed) during one minute on a baropodometer plate to acquire center-of-pressure (COP) oscillations and with electromyography (EMG) recording. The root mean square (RMS) of EMG was calculated. COP oscillations were higher with IRL use than spontaneous and controlled breathing tasks, but not between spontaneous and controlled conditions. EMG activity of Tibialis anterior and Soleus muscles were higher with IRL use in comparison to spontaneous and controlled breathing conditions. In conclusion, IRL use influenced the postural control through increased postural sway and neuromuscular compensation of the lower limbs in older women.