Supine Research Articles

Blunted cardiac autonomic dynamics to active standing test in postmenopausal women.

Although both aging and menopause influence cardiovascular autonomic control, the effect of menopause per se remains unclear. The current study was undertaken to test the hypothesis that post-menopausal women (PMW) have a blunted cardiovascular autonomic adjustment to active standing compared to pre-menopausal women. Thus, we compared the heart rate variability (HRV) indexes from supine (SUP) to orthostatic (ORT) positions among young women (YW), young men (YM), older men (OM), and PMW. The participants rested for 10 min in SUP and then stood up and remained for 5 min in ORT. ECG was continuously recorded, and R-R time series of about 300 beats were analyzed using linear (spectral analysis) and non-linear (symbolic analysis) methods. The variation from SUP to ORT was calculated (Δ = ORT-SUP) for each HRV index. In SUP, no difference was found for any HRV index among groups. However, Δ0V% and ΔLFn (cardiac sympathetic modulation) were reduced in PWM compared to all groups (OM, YW, and YM), while Δ2UV% and ΔHFn (cardiac vagal modulation) were reduced in PMW than the younger group (YW and YM). No differences were found among the male groups (OM and YM). In light of our results, the cardiac autonomic dynamic response to orthostatic stress is blunted in post-menopausal women compared to younger women and older men, a finding that might be influenced not only by aging.

Body Position Dependent Participation of Abdominal and Thoracic Breathing Movements During the Breathing Cycle

Aims: Both abdominal and thoracic breathing movements play important roles in the mechanics of breathing, participating differently in various body positions with abdominal breathing having a greater role. Recent studies showed that an early proning position of awake, non-intubated patients during the COVID-19 pandemic, even during pregnancy (PMID: 32320506, PMID: 33309507, PMID: 34915799) significantly affected the ventilatory parameters and mortality of SARS-CoV-2 patients. Thus, we hypothesized that in different body positions the participation of abdominal (AB) and thoracic breathing (TB) during the complete respiratory cycle (CRC) is different. To test this, we measured the participation of AB and TB to the CRC in different body positions under resting conditions. Methods: In young participants (N=26) age between 18 and 24 (M=21.3±1.6), changes in abdominal and chest circumferences were measured using plethysmography respiratory belts, during inhalation and exhalation in standing (ST), sitting (SI), supine (SU), prone (PR), and all on fours (AF) body positions. Respiratory frequency was also measured. Results: In different positions, the contribution of AB and TB to CRC were significantly different (F(4,100)=4.999, p=0.004, η2p=0.17). AB was significantly higher than TB in all positions (p<0.001). More specifically, AB gradually increased, while TB gradually decreased in the following order: SU(AB/TB) = 74.8±12.9%/25.2%, ST = 69±16%/31%, PR = 66.8±20.2%/33.2%, SI = 65.5±14.8%/34.5%, AF = 61.1±15.1%/38.9%. A significantly higher value was measured in the SU position compared to AF (p<0.001) and SI (p=0.011) positions; PR and ST positions showed intermediate values, which were not significantly different from those yielded by either of the other positions. Respiratory frequency was similar in different body positions. Conclusions: These data show that different body positions significantly affect the participation of abdominal and thoracic breathing during resting condition, underscoring not only the importance of respiratory distress patients positioning during hospitalization, but its usefulness in developing a respiratory training plan for elite athletes to optimize their physical and mental performance in competitive sports. AK: Ministry of Innovation and Technology (MIT) of Hungary-NRDI TKP2020-NKA-17, TKP2021-EGA-37, and National Research, Development, and Innovation Offce (NKFIH) OTKA K 132596 K_19, and Hungarian Academy of Sciences, Post-Covid 2021-34, and HUN-REN-SU: 02068 of Hungary, JT: ÚNKP-22-4-II-SE-4 (JT), TKP2021-EGA-25. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The Impact of Head Position on Neurological and Histopathological Outcome Following Controlled Automated Reperfusion of the Whole Body (CARL) in a Pig Model.

Introduction: Based on extracorporeal circulation, targeted reperfusion strategies have been developed to improve survival and neurologic recovery in refractory cardiac arrest: Controlled Automated Reperfusion of the whoLe Body (CARL). Furthermore, animal and human cadaver studies have shown beneficial effects on cerebral pressure due to head elevation during conventional cardiopulmonary resuscitation. Our aim was to evaluate the impact of head elevation on survival, neurologic recovery and histopathologic outcome in addition to CARL in an animal model. Methods: After 20 min of ventricular fibrillation, 46 domestic pigs underwent CARL, including high, pulsatile extracorporeal blood flow, pH-stat acid-base management, priming with a colloid, mannitol and citrate, targeted oxygen, carbon dioxide and blood pressure management, rapid cooling and slow rewarming. N = 25 were head-up (HUP) during CARL, and N = 21 were supine (SUP). After weaning from ECC, the pigs were extubated and followed up in the animal care facility for up to seven days. Neuronal density was evaluated in neurohistopathology. Results: More animals in the HUP group survived and achieved a favorable neurological recovery, 21/25 (84%) versus 6/21 (29%) in the SUP group. Head positioning was an independent factor in neurologically favorable survival (p < 0.00012). Neurohistopathology showed no significant structural differences between HUP and SUP. Distinct, partly transient clinical neurologic deficits were blindness and ataxia. Conclusions: Head elevation during CARL after 20 min of cardiac arrest independently improved survival and neurologic outcome in pigs. Clinical follow-up revealed transient neurologic deficits potentially attributable to functions localized in the posterior perfusion area, whereas histopathologic findings did not show corresponding differences between the groups. A possible explanation of our findings may be venous congestion and edema as modifiable contributing factors of neurologic injury following prolonged cardiac arrest.

Cerebral hemodynamic effects of head-up CPR in a porcine model

AimTo assess the hemodynamic effects of head elevation on cerebral perfusion during cardiopulmonary resuscitation (CPR) in a porcine model of cardiac arrest. MethodsVF was induced in eight 65 kg pigs that were treated with CPR after five minutes of no flow. Mean arterial pressure (MAP) was measured at the descending thoracic aorta. Internal carotid artery blood flow (CBF) was measured with an ultrasound probe. Cerebral perfusion pressure (CerPP) was calculated in two ways (CerPPICAP and CerPPreported) using the same intracranial pressure (ICP) measurement. CePPreported was calculated as MAP-ICP. CerPPICAP was calculated by using intracranial arterial pressure (ICAP) – ICP. The animals were switched between head up (HUP) and supine (SUP) CPR every five minutes for a total of twenty minutes of resuscitation. ResultsMAP and coronary perfusion pressure measurements were similar in both CPR positions (p = 0.36 and p = 0.1, respectively). ICP was significantly lower in the HUP CPR group (14.7 ± 1 mm Hg vs 26.9 ± 1 mm Hg, p < 0.001) as was ICAP (30.1 ± 2 mm Hg vs 42.6 ± 1 mmHg, p < 0.001). The proportional decrease in ICP and ICAP resulted in similar CerPPICAP comparing HUP and SUPCPR (p = 0.7). CBF was significantly lower during HUPCPR when compared to SUPCPR (58.5 ± 3 ml/min vs 78 ± 4 ml/min, p < 0.001). A higher CerPPreported was found during the HUP compared to SUP-CPR, when MAP was used (36.6 ± 2 mm Hg vs 23 ± 2 mm Hg, p < 0.001) without correcting for the hydrostatic pressure drop. ConclusionHUP did not affect cerebral perfusion pressure and it significantly decreased internal carotid blood flow.

Musculoskeletal demands in microsurgery-an explorative study comparing the ergonomics of microscope and 3D exoscope.

To assess neurosurgeons' physical demands and investigate ergonomic aspects when using microsurgical visualization devices. Six neurosurgeons performed micro-surgical procedures on cadaveric specimens using the prototype of a digital 3D exoscope system (Aeos®, Aesculap, Tuttlingen, Germany) and a standard operating microscope (Pentero 900, Zeiss, Oberkochen, Germany) at two different patient positions (semisitting (SS), supine (SP)). The activities of the bilateral upper trapezius (UTM), anterior deltoid (ADM), and lumbar erector spinae (LEM) muscles were recorded using bipolar surface electromyography and neck flexion, arm abduction, and arm anteversion angles by gravimetrical posture sensors. Perceived discomfort frequency was assessed and subjects compared the two systems in terms of usability, posture, physical and mental demands, and working precision. Using the exoscope led to reduced ADM activity and increased UTM and LEM activity during SS position. The neck was extended when using the exoscope system with lower arm anteversion and abduction angles during the SS position. Subjects reported discomfort at the shoulder-neck area less frequently and lower physical demands when using the Aeos®. However, mental demands were slightly higher and two subjects reported lower working precision. The exoscope system has the potential to reduce the activity of the ADM by changing surgeons arm posture which may be accompanied by less discomfort in the shoulder-neck area. However, dependent on the applied patient position higher muscle activities could occur in the UTM and LEM.

0443 Proposing a ‘projected apnea-hypopnea index (AHI)’ to mitigate intrinsic pitfalls of conventional AHI and testing its validity

Abstract Introduction The night-to-night variability of apnea-hypopnea index (AHI) can be explained by the fact that a person with OSA tends to spend less time in supine position and potentially less REM sleep, during which obstructive events could be a lot worse than in the other form. The primary aim of this study is to propose and test a “projected AHI” (pAHI) with which AHI can be mathematically adjusted for sleep position and sleep stage spent in a night of recording. Methods Using mathematical modeling explained in a separate abstract, a final pAHI formula was generated from polysomnography data of 337 subjects who exhibited all four sleep-types [combination of REM vs NREM and supine (SUP) vs non-supine (nSUP)] in one overnight study. A confusion matrix was generated using cutoffs of (p)AHI of 5 and hypothesizing pAHI being the gold standard and AHI being the test. Among subjects with borderline results (AHI of 5±3), sleep-type time and sleep-type AHI were compared between 4 groups of the confusion matrix to test the validity of the pAHI model. Results Out of 337 subjects with all four sleep-types, 119 subjects with AHI of 5±3 were identified and classified into a confusion matrix of no-OSA (43 TN, 10 FP), and OSA (13 FN, 53 TP). Actual sleep-type AHIs were in the order of increasing pAHI (TN, FP, FN, TP): 15.3, 29.2, 32.0, 34.8 for REMSUP; 4.00, 4.53, 4.73, 9.40 for REMnSUP; 2.83, 2.87, 9.38, 10.0 for NREMSUP; 0.44, 0.1, 1.06, 1.98 for NREMnSUP. Sleep time parameters were significantly different between no-OSA and OSA groups only when pAHI was used for diagnosis: %REMSUP (9.32 vs 5.39, p = 0.000009), %REMnSUP (8.08 vs 11.31, p = 0.002), %NREMSUP (48.13 vs 36.53, p = 0.001). %NREMnSUP (34.46 vs 46.77, p = 0.0002). Conclusion Without having to repeat a sleep study, projected AHI, by taking the effect of sleep position and sleep stages into account, can produce an AHI that mitigates night-to-night variability stemming from position and stage differences between nights. Projected AHI can be particularly useful in interpreting a sleep study with a borderline AHI result. Support (if any)

The effect of posture and exercise on blood CO kinetics during the optimized carbon monoxide rebreathing procedure

An indispensable precondition for the determination of hemoglobin mass (Hbmass) and blood volume by CO rebreathing is complete mixing of CO in the blood. The aim of this study was to demonstrate the kinetics of CO in capillary and venous blood in different body positions and during moderate exercise. Six young subjects (4 male, 2 female) performed three 2-min CO rebreathing tests in seated (SEA) & supine (SUP) positions as well as during moderate exercise (EX) on a bicycle ergometer. Before, during, and until 15 min after CO rebreathing cubital venous and capillary blood samples were collected simultaneously and COHb% was determined. COHb% kinetics were significantly slower in SEA than in SUP or EX. Identical COHb% in capillary and venous blood were reached in SEA after 5.0 ± 2.3 min, in SUP after 3.2 ± 1.3 min and in EX after 1.9 ± 1.2 min (EX vs. SEA p < .01, SUP vs. SEA p < .05). After 7th min, Hbmass did not differ between the resting positions (capillary: SEA 766 ± 217 g, SUP 761 ± 227 g; venous: SEA 759 ± 224 g, SUP 744 ± 207 g). Under exercise, however, a higher Hbmass (p < .05) was determined (capillary: 823 ± 221 g, venous: 804 ± 226 g). In blood, the CO mixing time in the supine position is significantly shorter than in the seated position. By the 6th minute complete mixing is achieved in either position giving similar Hbmass determinations. CO-rebreathing under exercise conditions, however, leads to ∼7% higher Hbmass values.

Posicionamentos de recém-nascidos prematuros e parâmetros fisiológicos – um estudo clínico randomizado

Abstract Introduction Multiple studies have shown the effects of prone (PP), supine (SP) and kangaroo (KP) positions on clinical and physiological outcomes in preterm newborns, but none compared these three types of positioning between them. Objective To investigate the influence of these positionings on heart rate, respiratory rate, peripheral oxygen saturation (SpO2) and alertness status in clinically stable preterm newborns (NBs) admitted to a neonatal intensive care unit. Methods In a randomized clinical trial, clinically stable NBs with gestational ages from 30 to 37 weeks who were breathing spontaneously were allocated in three positioning groups: PP, SP and KP. Heart rate, breathing frequency, SpO2 and alertness status were evaluated immediately before and after 30 minutes of positioning. Results In all, 66 NBs were assessed (corrected age: 35.48 ± 1.94 weeks; weight: 1840.14 ± 361.09 g), (PP: n = 22; SP: n = 23; KP: n = 21). NBs in the PP group showed a significant improvement in peripheral SpO2 (97.18 ± 2.16 vs 95.47 ± 2.93 vs 95.57 ± 2.95, p = 0.03) compared with the SP and KP groups. Conclusion In clinically stable preterm NBs, the PP was associated with better peripheral oxygen saturation than the SP or KP. In addition, there was a reduction in heart rate within prone position group and in the KP group there was an increase in the number of NBs in the deep sleep classification.

Feeding intolerance during prolonged prone position in overweight and obese patients with severe COVID-19.

the aim of this study was to compare the incidence rate of feeding intolerance (FI) during supine (SP) or prone positioning (PP) in critically ill COVID-19 patients. this was a retrospective cohort study of critically ill patients with overweight or obesity who received enteral nutrition (EN) in prone or supine positioning continuously during the first five days of mechanical ventilation. Nutritional risk, anthropometric measurements and body composition were assessed at the first 24 hours upon Intensive Care Unit (ICU) admission. Biochemical and clinical variables (Sequential Organ Failure Assessment [SOFA], Acute Physiology and Chronic Health Evaluation II [APACHE II], Acute Kidney Injury [AKI] or comorbidities diagnosis) were collected. Pharmacotherapy (prokinetics, sedatives or neuromuscular blocking agents) and FI incidence (gastric residual volume [GRV] ≥ 200 ml or ≥ 500 ml, vomiting or diarrhea) were daily recorded. Constipation was defined as the absence of evacuation for five consecutive days. eighty-two patients were included. Higher rate of prophylactic prokinetic prescription was observed in PP (42.8 vs 12.5 %, p = 0.002). GRV ≥ 200 in supine position was not different when compared to PP (p = 0.47). Vomiting episodes in supine compared to PP showed no difference between groups (15 % vs 24 %, p = 0.31). No differences in diarrhea events were detected (10 % vs 4.7 %, p = 0.36). Constipation was common in both groups (95 % vs 82 %, p = 0.06). FI during prone position was not different in comparison to supine position. Routinely use of prokinetics in continuous prone position may help to prevent FI incidence. Algorithm development is necessary for FI prevention and treatment so to avoid EN interruptions and adverse clinical outcomes.

Total hip replacement performed via a direct anterior approach: A comparison of the lateral and supine position

BackgroundThe direct anterior approach (DA) is a recognised approach for performing a total hip replacement (THR). Proponents cite improved recovery times, lower pain levels and improved patient satisfaction in the early post operative period. The procedure can be performed in the supine or lateral position. We wanted to compare the direct anterior approach in lateral decubitus (LD) position and supine (SU) position. MethodsSingle site, non-randomised, multiple surgeon retrospective cohort study between 2014 and 2021 to compare outcomes, complications and implant position for patients undergoing DAA THR in the SU or LD position. ResultsA total of 39 patients (22 lateral/17 supine) were identified. Patients had an average follow up of 45 months (17–81). 95% of the cohort were ASA 1 or 2. The majority of cases were uncemented (95%). A greater implant selection was used in the lateral group and the supine group used mainly implants associated with the supine table. No significant differences were found in post operative oxford hip scores, haemoglobin, length of stay, operative time, cup inclination, offset or post operative leg length. There were no recorded intra-operative complications in the LA group and two in the SU group – one calcar fracture and one canal perforation. No patient in either group has undergone a revision procedure. ConclusionBoth the supine and lateral position have resulted in satisfactory patient and radiological outcomes. We identified a higher rate of intra-operative fracture in the supine group which is comparable with existing literature. Given the similar outcomes between both groups we would suggest that surgeons wishing to consider the DAA may consider performing this in the lateral position as this will be more familiar to them, they will be able to use their existing implants and do not need a specialised operating table.

Effect of body posture on stability and balance of occlusal contacts

ABSTRACT Objective To evaluate the effect of body posture on occlusal contact. Methods A total of 30 healthy subjects were evaluated. T-Scan™ III was used to analyze the center of occlusal force (COF) and occlusal force distribution while subjects remained supine (SP), upright sitting with the head fixed (UP-HFI), upright sitting with the head free (UP-HFR), and natural standing (NS). Results The total trajectory length of COF was significantly longer in NS than in SP, UP-HFI, and UP-HFR. The COF area was significantly larger in UP-HFR than in SP and UP-HFI and also significantly larger in NS than in SP, UP-HFI, and UP-HFR. The anteroposterior occlusal force distribution (AOD) in NS shifted significantly forward, compared to SP, UP-HFI, and UP-HFR. AOD in UP-HFI and UP-HFR shifted significantly forward, compared to the SP position. Conclusion Changes in body posture affect the stability and anteroposterior balance of occlusal contacts.

The prevalence of redundant nerve roots in standing positional MRI decreases by half in supine and almost to zero in flexed seated position: a retrospective cross-sectional cohort study

PurposeThis retrospective cross-sectional cohort study investigated the influence of posture on lordosis (LL), length of the spinal canal (LSC), anteroposterior diameter (APD L1-L5), dural cross-sectional area (DCSA) of the lumbar spinal canal, and the prevalence of redundant nerve roots (RNR) using positional magnetic resonance imaging (MRI) (0.6 T).MethodsSixty-eight patients with single-level degenerative central lumbar spinal stenosis (cLSS) presenting with RNR in the standing position (STA) were also investigated in supine (SUP) or neutral seated (SIT) and flexed seated (FLEX) positions. Additionally, 45 patients complaining of back pain and without MRI evidence of LSS were evaluated. Statistical significance was set at p < 0.05.ResultsControls (A) and patients with cLSS (B) were comparable in terms of mean age (p = 0.88) and sex (p = 0.22). The progressive transition from STA to FLEX led to a comparable decrease in LL (p = 0.97), an increase in LSC (p = 0.80), and an increase in APD L1-L5 (p = 0.78). The APD of the stenotic level increased disproportionally between the different postures, up to 67% in FLEX compared to 29% in adjacent non-stenotic levels (p < 0.001). Therefore, the prevalence of RNR decreased to 49, 26, and 4% in SUP, SIT, and FLEX, respectively.ConclusionThe prevalence of RNR in standing position was underestimated by half in supine position. Body postures modified LL, LSC, and APD similarly in patients and controls. Stenotic levels compensated for insufficient intraspinal volume with a disproportionate enlargement when switching from the STA to FLEX.

The Systolic Pulmonary Arterial Pressure Liaises Impaired Cardiac Autonomic Control to Pro-inflammatory Status in Systemic Sclerosis Patients.

The current study was undertaken to test the hypothesis that systemic sclerosis (SSc) patients with higher systolic pulmonary arterial pressures (PAPs) present a blunted cardiac autonomic modulation and a pro-inflammatory profile. Thirty-nine SSc patients were enrolled (mean age 57 ± 11 years). ECG and respiration were recorded in the supine (SUP) position and during the active standing (ORT). Heart rate variability (HRV) analysis was performed on samples of 300 beats. The symbolic analysis identified three patterns, 0V%, (sympathetic) and 2UV% and 2LV%, (vagal). The %ΔORT was calculated from the differences between HRV in ORT and SUP, normalized (%) by the HRV values at rest. The PAPs was obtained non-invasively through echocardiography. For the inter-group analysis, participants were allocated in groups with higher (+PAPs ≥ median) and lower PAPs (–PAPs < median) values. At rest, the cardiac sympathetic modulation (represented by 0V%) was positively correlated with PAPs, while parasympathetic modulation (represented by 2LV%) was negatively correlated with PAPs. The dynamic response to ORT (represented by Δ0V% and Δ2LV%), sympathetic and parasympathetic were negatively and positively correlated with PAPs, respectively. The +PAPs group presented a higher inflammatory status and a blunted cardiac autonomic response to ORT (↓Δ0V% and ↑Δ2LV%) compared to the –PAPs group. These findings suggest an interplay among cardiac autonomic control, inflammatory status, and cardiopulmonary mechanics that should be considered for the assessment, monitoring, and treatment of SSc patients.

Differences in neck muscle activity according to lying positions using a smartphone.

Due to the extended use of smartphones, people spend a lot of time on these devices while lying down. The purpose of the present study was to compare the differences in neck muscle activity of participants while they watched videos on a smartphone in four different lying positions (supine (SUP), prone on elbows (PE), side lying (SIDE), and 45∘ head turn while side lying (45-SIDE)). Twenty-three healthy volunteers (22.4 ± 1.7 years) were enrolled in this study. We assessed the activities of their right and left sternocleidomastoid (SCM), anterior scalene, cervical erector spinae (CES), and upper trapezius (UT) muscles while they watched videos on a smartphone in four different lying positions. The right and left SCM and CES had significantly different muscle activities depending on the lying positions. The SCM activity had a significantly greater asymmetry in the 45-SIDE position, while the CES activity had a significantly greater asymmetry in the SIDE and 45-SIDE positions. Moreover, the UT activity had a significantly greater asymmetry in the SUP, PE, and SIDE positions. Neck muscle activity and asymmetry were the lowest in the SUP position relative to the other positions. Therefore, lying down in the SUP position may minimize neck muscle activation while using a smartphone.

The influence of three different test positions and thigh asymmetry on measurements of isometric hip flexion strength in men and women

Purpose: The aim of this study was to compare muscle strength at 90° hip and knee flexion as measured in three different positions and to investigate whether an internal or external deficit in the range of rotation in the hip joint affects flexor muscle strength. Methods: We measured the peak muscle torque of rotation in the hip joint, using isometric torquemeter, and hip ROM in healthy participants N = 40, aged 21.6 ± 1.9, in three different measurement positions. We tested for differences between the positions, and for the potential influence of participant’s sex and ROM asymmetry. Results: The measured peak muscle torque was affected not only by sex and the value of hip flexion affect, but also by the position in which it is measured. Subjects with restricted external rotation of the hip joint (CERD) had significantly higher flexor peak muscle torque compared to subjects with restricted internal rotation (CIRD), in all but the supine position. For CERD, the results were: Supine (SuP) 1.02 ± 0.26; Sitting (StP) 1.32 ± 0.58; Standing (SP) 1.53 ± 0.47; and for CIRD, the results were: Supine (SuP) 1.05 ± 0.17; Sitting (StP) 1.05 ± 0.40; Standing (SP) 1.47 ± 0.53. Conclusions: Overall, measurement position and passive ROM significantly influence the peak muscle torque in isometric conditions. Moreover, an imbalance in thigh rotation movement significantly determines the magnitude of muscle torque of the hip flexion movement. Individuals with increased internal-toexternal rotation achieved significantly higher values for flexor muscle torque force moments. Overall, these findings are of importance for interpreting or comparing any reported values for muscle torque force moments

The effect of the head-up position on cardiopulmonary resuscitation: a systematic review and meta-analysis

ObjectiveExperimental studies of head-up positioning (HUP) during cardiopulmonary resuscitation (CPR) have had some degree of conflicting published results. The current study aim was to analyze and reconcile those discrepancies in order to better clarify the effects of HUP CPR compared to conventional supine (SUP) CPR.MethodsThree databases (PubMed, EMBASE and Cochrane Library) were searched comprehensively (from each respective database's inception to May 2021) for articles addressing HUP CPR. The primary outcome to be observed was cerebral perfusion pressure (CerPP), and secondary outcomes were mean intracranial pressure (ICP), mean arterial pressure (MAP), coronary perfusion pressure (CoPP) and frequencies of return of spontaneous circulation (ROSC).ResultsSeven key studies involving 131 animals were included for analysis. Compared to SUP CPR, CerPP (MD 10.37; 95% CI 7.11–13.64; p < 0.01; I2 = 58%) and CoPP (MD 7.56; 95% CI 1.84–13.27, p = 0.01; I2 = 75%) increased significantly with HUP CPR, while ICP (MD − 13.66; 95% CI − 18.6 to –8.71; p < 0.01; I2 = 96%) decreased significantly. Combining all study methodologies, there were no significant differences detected in MAP (MD − 1.63; 95% CI − 10.77–7.52; p = 0.73; I2 = 93%) or frequency of ROSC (RR 0.9; 95% CI 0.31–2.60; p = 0.84; I2 = 65%). However, in contrast to worse outcomes in studies using immediate elevation of the head in a reverse Trendelenburg position, study outcomes were significantly improved when HUP (head and chest only) was introduced in a steady, graduated manner following a brief period of basic CPR augmented by active compression–decompression (ACD) and impedance threshold (ITD) devices.ConclusionIn experimental models, gradually elevating the head and chest following a brief interval of circulatory priming with ACD and ITD devices can enhance CoPP, lower ICP and improve CerPP significantly while maintaining MAP. This effect is immediate, remains sustained and is associated with improved outcomes.

Superimposed High Frequency Jet Ventilation Minimises Diaphragm, Bronchus, and Mediastinum Motion during One-Lung Flooding

Background: One-Lung Flooding (OLF) represents an ideal acoustic pathway for focused ultrasound ablation of lung tumours. Despite stabilization of the adjacent hemidiaphragm by OLF, standard Pressure-Controlled Ventilation (PCV) of the contralateral lung causes an unacceptable movement of the flooded lung. We examined whether Superimposed High Frequency Jet Ventilation (SHFJV) reduces lung motion compared to PCV during OLF. Methods: The study included 15 pigs: 10 underwent OLF; 5 controls underwent two-lung ventilation without OLF. Using ultrasound, diaphragm displacement on the flooded lung side was measured during PCV and SHFJV in the left lateral (LLP), Supine (SP), and Right Lateral Positions (RLP). Bronchus and mediastinum displacements were measured in the right lateral position. Results: Diaphragm displacement on the flooded lung side was significantly reduced during SHFJV, compared with PCV, in all animal positions (LLP: 7mm [4.75-8.0] vs. 17mm [14.75-19.0], P=0.0039; SP: 4mm [3.75-4.25] vs. 17mm [16.0–18.5], P=0.0039; RLP: 8mm [5.75-9.0] vs. 20mm [14.0-23.25], P=0.0078). Displacement of both the bronchus and mediastinum were significantly reduced during SHFJV, compared with PCV, in RLP (bronchus: 2.0mm [1.75-2.25] vs. 3.0mm [2.75-3.0], P=0.027; mediastinum: 4.5mm [4.0-5.0] vs. 10mm [7.0-10.0], P=0.0078. Conclusion: Thus, SHFJV minimises diaphragm, bronchus, and mediastinum motion during OLF, which is a prerequisite for effective lung tumour ablation.

Abnormal Sympathetic Responses To Orthostasis After Concussion Explored Through Blood Pressure Variability

PURPOSE: Orthostasis causes a gravity-dependent redistribution of blood volume to the lower extremities. The baroreflex coordinates an effector response through the sympathetic nervous system (SNS) to the peripheral vasculature to buffer changes in systolic blood pressure (SBP). In autonomic dysfunction (AD), impaired or exaggerated responses may lead to orthostatic hypotension (OHypo) or hypertension (OHTN). AD is becoming an increasingly recognized consequence of an acute concussion injury. The purpose of this study was to evaluate the SNS responses to orthostasis in recently concussed athletes. METHODS: A prospective study was performed in 32 concussed college athletes (gender: 22 female, 10 male; age: 20 ± 1 yrs; height: 1.74 ± 0.11 m; weight: 74 ± 13 kg) and 14 athlete controls (gender: 8 female, 6 male; age: 20 ± 2 yrs; height: 1.70 ± 0.10 m; weight: 69 ± 13 kg). Beat-to-beat SBP was assessed digitally at rest for 10 minutes in the supine (SUP) position and then for 3 minutes in the standing (STND) position within 48 hours (48H) of concussion. The change in SBP (ΔSBP) was computed from the difference between SUP and the final 15 seconds of STND. ΔSBP was then categorized as Normal (NR: ΔSBP -19 to +19 mmHg); OHypo (SBP fall ≥20 mmHg); and, OHTN (SBP rise ≥20 mmHg) for each group. Fast-Fourier transform was performed and power calculated for the total, very low, low and high frequency power (TP, vLF, LF and HF, respectively) spectra in each position; the variables were log10 transformed for parametric analyses. RESULTS: Fourteen control and 14 concussion participants had a NR ΔSBP, whereas 11 concussion participants had OHypo and 7 had OHTN. There were no differences across these four groups for the TP, vLF, LF, and HF in the SUP position. In the STND position, TP (p < 0.0001), vLF (p < 0.0001), and HF (p < 0.05) were significant for the omnibus model. Bonferroni post hoc analyses revealed that the OHypo concussion group had a significantly lower TP and vLF than each of the 3 other groups, and the OHTN concussion group had a significant elevation and trend toward a significant elevation of HF compared to the OHypo and NR concussion groups, respectively. CONCLUSIONS: Different mechanisms appear to contribute to and influence AD during orthostasis within 48H of concussion injury.

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 decreased αLF 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.

The Physical Capacity of Rowing Athletes Cannot Reverse the Influence of Age on Heart Rate Variability during Orthostatic Stress.

The current study was undertaken to test the hypothesis that the high physical capacity of rowing athletes may not reverse the influence of age on cardiac autonomic control decline estimated by heart rate variability (HRV). Forty-four male subjects divided in four groups: 11 young athletes (YA; 18 ±1 year), 11 young non-athletes (YNA; 20 ±1 year), 11 middle age athletes (MAA; 43 ±6 years) and 11 middle age non-athletes (MNA; 44 ±8 years) participated in the study. Heart rate (HR) was recorded beat-by-beat for 10 minutes in supine (SUP) and 10 min in orthostatic (ORT) positions. HRV was analyzed in the frequency domain to obtain the spectral power in the high (HF) and low frequency (LF) bands, and the changes to ORT (%∆HRV) were calculated (ORT - SUP / SUP). During SUP, HF was lower in MNA and MA compared to YA and YNA, while LF was lower in MNA than YA. For %ΔHRV, %ΔHF was higher in YA than YNA, MA and MNA. The %ΔLF was not different among groups. In conclusion, aging seems to overcome the influence of physical fitness on neural regulation of the heart, as highlighted by the HRV response to active standing.