Background: Chronic pain is closely associated with dysregulation of the autonomic nervous system, often reflected by reduced heart rate variability (HRV). While observational studies have demonstrated this association, the extent to which pain interventions modulate HRV and the impact of individual factors on HRV changes remain unclear. Objective: To evaluate the impact of pain interventions on HRV parameters through meta-analysis of randomized controlled trials (RCTs), and to examine whether intervention type and individual factors such as body mass index (BMI) moderate HRV responses. Methods: We conducted a systematic review of 23 RCTs and a meta-analysis of 21 RCTs (1262 subjects) involving patients with acute and chronic pain. HRV outcomes were extracted pre- and post-intervention. Both between-group (active vs. sham/control) and one-group (pre-post within active group) analyses were performed for time-domain indices—standard deviation of normal-to-normal intervals (SDNN), root mean square of successive differences (RMSSD), and percentage of successive normal-to-normal intervals > 50 ms (pNN50)—and frequency-domain indices—high-frequency (HF) and low-frequency (LF) components. Meta-regressions tested moderators including BMI, age, and pain phenotype. The protocol was registered in PROSPERO (CRD42023448264). Results: Twenty-three RCTs involving 1262 participants with a wide range of pain conditions were included. Meta-analysis of time-domain HRV parameters showed a trend toward improvement: SDNN (g = 0.435, p = 0.059) approached significance, while RMSSD (g = 0.361, p = 0.099) and pNN50 (g = 0.222, p = 0.548) showed smaller, non-significant effects. Frequency-domain analysis revealed a significant moderate reduction in the LF/HF ratio (g = −0.378, p = 0.003), suggesting a shift toward parasympathetic dominance. HF and LF showed small, non-significant changes. One-group meta-analysis confirmed significant improvements in vagally mediated HRV, with large effects for RMSSD (g = 1.084, p < 0.001) and HF (g = 0.622, p < 0.001), and a moderate effect for SDNN (g = 0.455, p = 0.004). Meta-regression identified BMI as a significant moderator: higher BMI was associated with attenuated improvements in HF and RMSSD and a slight shift toward sympathetic predominance. Conclusions: Pain interventions can significantly modulate autonomic function, as reflected in HRV improvements, particularly in vagally mediated indices. These effects are influenced by patient characteristics such as BMI. HRV may serve as a valuable biomarker for both treatment efficacy and autonomic recovery in pain management. In this context, HRV highlights its role as a biomarker for pain dysregulation and compensatory failure, reflecting shared top-down modulation between nociception and autonomic regulation.

International recommendations propose the presence of physiotherapists with specialized training in critical patients, available 24 hours a day and 7 days a week (24/7-PT) in the Intensive Care Unit (ICU), with a standardized physiotherapist/patient ratio of 1 per 5 beds in high complexity units. It is unknown if the organizational characteristics of the ICUs are related to the adherence with these recommendations. Objective: To determine the relationship between the organizational characteristics and the adherence of international recommendations of physiotherapy care, in adult ICUs at a national level. Methods: Secondary database analysis, with information from 86% of adult Chilean ICUs. The organizational characteristics (origin of the ICU, number of beds, level of complexity and technical-administrative dependency of the physiotherapist) were related to 24/7-PT availability, physiotherapist/patient ratio of 1 per 5 beds and presence of physiotherapy specialists. Results: Out of 64 adult ICUs, a 70% (n=45) have 24/7-PT availability. Physiotherapist/patient ratio was observed during weekdays in half of the private centers during day shifts. Presence of physiotherapy specialists was detected in 31% of the private sector. Significant differences were found between the number of beds and the probability to accomplish 24/7-PT availability and physiotherapist/patient ratio (p<0.001 and p=0.34 respectively). The probability that a unit complies 24/7-PT availability differs significantly depending on the technical-administrative dependency (p<0.001). No significant relationship was found between the level of complexity and the adherence to the international recommendations. A greater adherence to 24/7-PT availability in public ICUs (OR 5.21, 95%CI 1.37-19.81) and when physiotherapist-dependence became the Critical Patients Unit (OR 6.59, 95%CI 1.41-30.80) was evidenced. Conclusions: The origin of the ICU and the technical-administrative dependence seem to be relevant for the compliance of 24/7-PT availability. Future studies should be aimed at identifying the causes of this relationship, in order to optimize the human resources in the ICU.

OBJECTIVES: This study aimed to explore whether airway closure can be detected in patients with severe acute bronchiolitis on invasive mechanical ventilation. DESIGN: Single-center prospective physiologic study carried out in 2023–2024. SETTING: PICU in a tertiary-care general hospital. PATIENTS: Infants with acute bronchiolitis undergoing invasive mechanical ventilation. INTERVENTIONS: Under deep sedation and neuromuscular blockade, the mechanical ventilator, in a volume-controlled mode, was transiently set with a respiratory rate of five breaths/min, a tidal volume of 6 mL/kg of ideal body weight, positive end-expiratory pressure 0 cm H₂O, a flow rate of 2 L/min, an inspiratory-expiratory ratio of 1:1, and a Fio ₂ of 1.0. After recording three breath cycles, the patient was returned to baseline ventilatory settings. MEASUREMENTS AND MAIN RESULTS: We identified the presence of airway closure through the low-flow pressure-volume curve obtained from a pneumotachometer with a flow sensor placed at the Y-piece and simultaneously from the pressure-impedance curve and ventilation maps acquired using electrical impedance tomography. We included 12 patients, and airway closure was detected in seven of them. The median (interquartile range [IQR]) airway opening pressure was 14 cm H₂O (IQR, 11–17 cm H₂O). Patients with airway closure exhibited high levels of driving pressure, with a median of 16 cm H₂O (IQR, 11–17 cm H₂O), and low levels of respiratory system compliance, with a median of 0.41 mL/cm H₂O/kg (IQR, 0.38–0.59 mL/cm H₂O/kg). When these parameters were corrected for airway opening pressure, there was a significant decrease in driving pressure to 9 cm H₂O (IQR, 8–12 cm H₂O; p = 0.018) and a significant increase in respiratory system compliance to 0.70 mL/cm H₂O/kg (IQR, 0.53–0.81 mL/cm H₂O/kg; p = 0.018). CONCLUSIONS: Airway closure requiring high opening pressures can be detected in ventilated infants with acute bronchiolitis, and this phenomenon may impact respiratory mechanics.

Background/Objectives: Chronic pain is associated with autonomic nervous system (ANS) dysfunction, which can be indexed by heart rate variability (HRV). This cross-sectional study examined associations between ANS dysregulation and phantom limb pain (PLP) intensity in amputees and explored related clinical and psychosocial variables. Methods: Fifty-three adults with chronic PLP (mean age 57.7 ± 15.4; 60% male) were enrolled. Primary exposure was PLP intensity concurrent with HRV time- and frequency-domain metrics. Additional variables included residual limb pain, phantom limb sensations (PLS), telescoping and PLP–PLS index. Results: PLP intensity was not significantly associated with frequency-domain HRV measures. Time-domain parameters RMSSD (root mean square of successive differences) and pNN50 (percentage of successive normal RR intervals >50 ms) were lower in the positive PLP–PLS group. In multivariate models, depression (range of βs:−1.36 to −58.16), pain-medication use (range of βs: −12.3 to −953.4), and body mass index (range of βs: 0.55 to 45.8) were significantly associated with lower SDNN (standard deviation of NN intervals), RMSSD, pNN50, low-frequency (LF), and high-frequency (HF) power. Female sex and pre-amputation pain correlated with higher LF, whereas traumatic etiology correlated with lower LF. Poor sleep quality correlated with elevated HF. No predictors related to the LF/HF ratio. Conclusions: HRV alterations in PLP were associated with depression and pain-medication use rather than pain intensity. Findings support HRV dysfunction as a marker of brain compensatory failure within the autonomic circuit, and maladaptive plasticity, highlighting utility for identifying central dysfunction even when pain severity does not vary.

Background/Objectives: Chronic pain is associated with autonomic nervous system (ANS) dysfunction. Heart rate variability (HRV) indexes sympathetic–parasympathetic balance and autonomic adaptability. Phantom limb pain (PLP) is prevalent after limb loss, but evidence of ANS dysregulation in chronic PLP is limited. This cross-sectional study examined associations between ANS dysregulation and PLP intensity in amputees and explored links with clinical and psychosocial variables. Methods: Fifty-three adults with chronic PLP (mean age 57.7±15.4; 60% male) were enrolled. Primary exposure was PLP intensity concurrent with HRV time- and frequency-domain metrics. Additional variables included residual limb pain, phantom limb sensations (PLS), and telescoping. The PLP–PLS index was also evaluated. Results: PLP intensity was not significantly associated with frequency-domain HRV measures. Time-domain parameters RMSSD (root mean square of successive differences) and pNN50 (percentage of successive normal RR intervals >50 ms) were lower in the positive PLP–PLS group. In multivariate models, depression, pain-medication use, and body mass index were associated with lower SDNN (standard deviation of NN intervals), RMSSD, pNN50, low-frequency (LF), and high-frequency (HF) power. Female sex and pre-amputation pain correlated with higher LF, whereas traumatic etiology correlated with lower LF. Poor sleep quality correlated with elevated HF. No predictors related to the LF/HF ratio. Conclusions: HRV alterations in PLP were associated with depression and pain-medication use rather than pain intensity. Findings support HRV dysfunction as a marker of brain compensatory failure and central neurophysiological disruption within circuits governing autonomic regulation and maladaptive plasticity, highlighting utility for identifying central dysfunction even when pain severity does not vary.