Digital technologies for step counting: between promises of reliability and risks of reductionism.

Step counting is among the fundamental features of wearable technology, as it grounds several uses of wearables in biomedical research and clinical care, is at the center of emerging public health interventions and recommendations, and is gaining increasing scientific and political importance. This paper provides a perspective of step counting in wearable technology, identifying some limitations to the ways in which wearable technology measures steps and indicating caution in current uses of step counting as a proxy for physical activity. Based on an overview of the current state of the art of technologies and approaches to step counting in digital wearable technologies, we discuss limitations that are methodological as well as epistemic and ethical-limitations to the use of step counting as a basis to build scientific knowledge on physical activity (epistemic limitations) as well as limitations to the accessibility and representativity of these tools (ethical limitations). As such, using step counting as a proxy for physical activity should be considered a form of reductionism. This is not per se problematic, but there is a need for critical appreciation and awareness of the limitations of reductionistic approaches. Perspective research should focus on holistic approaches for better representation of physical activity levels and inclusivity of different user populations.

Non-invasive assessment of fatigue and recovery of inspiratory rib cage muscles during endurance test in healthy individuals.

INTRODUCTION: Fatigue is defined as loss of capacity to develop muscle force and/or velocity that is reversible at rest. We assessed non-invasively the fatigue and recovery of inspiratory rib cage muscles during two respiratory endurance tests in healthy individuals. METHODS: The sniff nasal inspiratory pressure (SNIP) was assessed before and after two respiratory endurance tests: normocapnic hyperpnea (NH) and inspiratory pressure threshold loading (IPTL). Contractile (maximum rate of pressure development and time to peak pressure) and relaxation parameters (maximum relaxation rate [MRR], time constant of pressure decay [τ], and half relaxation time) obtained from sniff curves and shortening velocity and mechanical power estimated using optoelectronic plethysmography were analyzed during SNIP maneuvers. Respiratory muscle activity (electromyography) and tissue oxygenation (near-infrared spectroscopy-NIRS) were obtained during endurance tests and SNIP maneuvers. Fatigue development of inspiratory rib cage muscles was assessed according to the slope of decay of median frequency. RESULTS: Peak pressure during SNIP decreased after both protocols (p <0.05). MRR, shortening velocity, and mechanical power decreased (p <0.05), whereas τ increased after IPTL (p <0.05). The median frequency of inspiratory rib cage muscles (i.e., sum of sternocleidomastoid, scalene, and parasternal) decreased linearly during IPTL and exponentially during NH, mainly due to the sternocleidomastoid. CONCLUSION: Fatigue development behaved differently between protocols and relaxation properties (MRR and τ), shortening velocity, and mechanical power changed only in the IPTL.

The Manual Diaphragm Release Technique improves diaphragmatic mobility, inspiratory capacity and exercise capacity in people with chronic obstructive pulmonary disease: a randomised trial.

QUESTIONS: In people with chronic obstructive pulmonary disease, does the Manual Diaphragm Release Technique improve diaphragmatic mobility after a single treatment, or cumulatively? Does the technique also improve exercise capacity, maximal respiratory pressures, and kinematics of the chest wall and abdomen? DESIGN: Randomised, controlled trial with concealed allocation, intention-to-treat analysis, and blinding of participants and assessors. PARTICIPANTS: Twenty adults aged over 60 years with clinically stable chronic obstructive pulmonary disease. INTERVENTION: The experimental group received six treatments with the Manual Diaphragm Release Technique on non-consecutive days within a 2-week period. The control group received sham treatments following the same regimen. OUTCOME MEASURES: The primary outcome was diaphragmatic mobility, which was analysed using ultrasonography. The secondary outcomes were: the 6-minute walk test; maximal respiratory pressures; and abdominal and chest wall kinematics measured by optoelectronic plethysmography. Outcomes were measured before and after the first and sixth treatments. RESULTS: The Manual Diaphragm Release Technique significantly improved diaphragmatic mobility over the course of treatments, with a between-group difference in cumulative improvement of 18mm (95% CI 8 to 28). The technique also significantly improved the 6-minute walk distance over the treatment course, with a between-group difference in improvement of 22 m (95% CI 11 to 32). Maximal expiratory pressure and sniff nasal inspiratory pressure both showed significant acute benefits from the technique during the first and sixth treatments, but no cumulative benefit. Inspiratory capacity estimated by optoelectronic plethysmography showed significant cumulative benefit of 330ml (95% CI 100 to 560). The effects on other outcomes were non-significant or small. CONCLUSION: The Manual Diaphragm Release Technique improves diaphragmatic mobility, exercise capacity and inspiratory capacity in people with chronic obstructive pulmonary disease. This technique could be considered in the management of people with chronic obstructive pulmonary disease. TRIAL REGISTRATION: NCT02212184.

Blood flow does not redistribute from respiratory to leg muscles during exercise breathing heliox or oxygen in COPD.

In patients with chronic obstructive pulmonary disease (COPD), one of the proposed mechanisms for improving exercise tolerance, when work of breathing is experimentally reduced, is redistribution of blood flow from the respiratory to locomotor muscles. Accordingly, we investigated whether exercise capacity is improved on the basis of blood flow redistribution during exercise while subjects are breathing heliox (designed to primarily reduce the mechanical work of breathing) and during exercise with oxygen supplementation (designed to primarily enhance systemic oxygen delivery but also to reduce mechanical work of breathing). Intercostal, abdominal, and vastus lateralis muscle perfusion were simultaneously measured in 10 patients with COPD (forced expiratory volume in 1 s: 46 ± 12% predicted) by near-infrared spectroscopy using indocyanine green dye. Measurements were performed during constant-load exercise at 75% of peak capacity to exhaustion while subjects breathed room air and, then at the same workload, breathed either normoxic heliox (helium 79% and oxygen 21%) or 100% oxygen, the latter two in balanced order. Times to exhaustion while breathing heliox and oxygen did not differ (659 ± 42 s with heliox and 696 ± 48 s with 100% O2), but both exceeded that on room air (406 ± 36 s, P < 0.001). At exhaustion, intercostal and abdominal muscle blood flow during heliox (9.5 ± 0.6 and 8.0 ± 0.7 ml · min(-1)·100 g(-1), respectively) was greater compared with room air (6.8 ± 0.5 and 6.0 ± 0.5 ml·min(-1)·100 g·, respectively; P < 0.05), whereas neither intercostal nor abdominal muscle blood flow differed between oxygen and air breathing. Quadriceps muscle blood flow was also greater with heliox compared with room air (30.2 ± 4.1 vs. 25.4 ± 2.9 ml·min(-1)·100 g(-1); P < 0.01) but did not differ between air and oxygen breathing. Although our findings confirm that reducing the burden on respiration by heliox or oxygen breathing prolongs time to exhaustion (at 75% of maximal capacity) in patients with COPD, they do not support the hypothesis that redistribution of blood flow from the respiratory to locomotor muscles is the explanation.

Acute effects of volume-oriented incentive spirometry on chest wall volumes in patients after a stroke.

BACKGROUND: The aim of the present study was to assess how volume-oriented incentive spirometry applied to patients after a stroke modifies the total and compartmental chest wall volume variations, including both the right and left hemithoraces, compared with controls. METHODS: Twenty poststroke patients and 20 age-matched healthy subjects were studied by optoelectronic plethysmography during spontaneous quiet breathing (QB), during incentive spirometry, and during the recovery period after incentive spirometry. RESULTS: Incentive spirometry was associated with an increased chest wall volume measured at the pulmonary rib cage, abdominal rib cage and abdominal compartment (P = .001) and under 3 conditions (P < .001). Compared with healthy control subjects, the tidal volume (VT) of the subjects with stroke was 24.7, 18.0, and 14.7% lower during QB, incentive spirometry, and postincentive spirometry, respectively. Under all 3 conditions, the contribution of the abdominal compartment to VT was greater in the stroke subjects (54.1, 43.2, and 48.9%) than in the control subjects (43.7, 40.8, and 46.1%, P = .039). In the vast majority of subjects (13/20 and 18/20 during QB and incentive spirometry, respectively), abdominal expansion precedes rib cage expansion during inspiration. Greater asymmetry between the right and left hemithoracic expansions occurred in stroke subjects compared with control subjects, but it decreased during QB (62.5%, P = .002), during incentive spirometry (19.7%), and postincentive spirometry (67.6%, P = .14). CONCLUSIONS: Incentive spirometry promotes increased expansion in all compartments of the chest wall and reduces asymmetric expansion between the right and left parts of the pulmonary rib cage; therefore, it should be considered as a tool for rehabilitation.

Chest wall volume changes during inspiratory loaded breathing.

We assessed the effect of inspiratory loaded breathing (ILB) on respiratory muscle strength and investigated the extent to which respiratory muscle fatigue is associated with chest wall volume changes during ILB. Twelve healthy subjects performed ILB at 76 ± 11% of maximal inspiratory mouth pressure (MIP) for 1h. MIP and breathing pattern during 3 min of normocapnic hyperpnea (NH) were measured before and after ILB. Breathing pattern and chest wall volume changes were assessed by optoelectronic plethysmography. After ILB, six subjects decreased MIP significantly (-16 ± 10%; p < 0.05), while the other six subjects did not (0 ± 7%, p = 0.916). Only subjects with decreased MIP after ILB lowered end-expiratory rib cage volume (volume at which inspiration is initiated) below resting values during ILB. During NH after ILB, tidal volume was smaller in subjects with decreased MIP (-19 ± 16%, p < 0.05), while it remained unchanged in the other group (-3 ± 11%, p = 0.463). These results suggest that respiratory muscle fatigue depends on the lung volume from which inspiratory efforts are made during ILB.