Effect of posture on regional ventilation in children.

Little information has been published concerning the pattern of regional ventilation in children, yet many differences in lung and chest wall mechanics in childhood, supported by clinical observation, have led to the hypothesis that the pattern of regional ventilation seen in children may not be the same as in adults. Forty-three children and 16 adult volunteers underwent Krypton (Kr) 81m radionuclide ventilation lung scans in the supine and right and left decubitus postures. In children aged 2-10 years mean fractional ventilation to the right lung (VfR) was 46.1%. This fell to 36% when dependent and rose to 56.1% in the uppermost position. Redistribution of ventilation away from the dependent towards the uppermost lung was seen in all children. In children aged 10-18 years VfR was 57.2% (supine), 48.0% (dependent), and 62.9% (uppermost). An identical pattern was seen in children with normal or abnormal pulmonary function tests (peak expiratory flow rate, and FEV1: FVC ratio). In subjects over 18 years of age a different pattern was seen: mean VfR was 52.4% (supine), rising to 53.4% (dependent), and falling to 48.9% (uppermost). Postural redistribution of ventilation, as assessed by Kr81m ventilation imaging, changes late in the second decade of life. This will have clinical consequences in the management of children with unilateral lung disease.     

Effect of posture on spontaneous and thermally stimulated cardiovascular oscillations

STUDY OBJECTIVE--The aim of the study was to investigate the effect of posture on thermally stimulated cardiovascular oscillations. DESIGN--The effect of increased gravitational stress (rising from sitting to standing position) on the thermally stimulated cardiovascular oscillations was measured in young male volunteers. Extensive cardiovascular function data were obtained using a cardiovascular investigation protocol. SUBJECTS--The volunteers were five fit young men, aged 20-21 years. EXPERIMENTS AND MAIN RESULTS--Cardiovascular changes from sitting to standing indicated increased sympathetic and decreased parasympathetic influence on heart and skin blood vessels; mean heart rate increased, beat to beat heart rate variability diminished, high frequency periodic heart rate variability decreased, low frequency heart rate oscillations and ratio of low frequency to high frequency heart rate variability increased, mean skin blood flow and oscillations of skin blood flow decreased (all p less than 0.05). Thermal skin stimulation at 0.01-0.10 Hz frequency increased both sitting and standing 0.10 Hz periodic heart rate variability (p less than 0.05), and 0.10 Hz thermal stimulation entrained the heart rate oscillations in sitting and standing subjects (p less than 0.05). In contrast, skin blood flow oscillations in sitting subjects decreased, while in standing subjects it increased during 0.10 Hz thermal stimulation compared to the corresponding prestimulus values (p less than 0.04). CONCLUSIONS--On the basis of previous physiological experiments, these results suggest coupling between thermoregulatory and 0.10 Hz reflex activities.     

Effect of posture on inter-regional distribution of pulmonary ventilation in man

Regional ventilation per unit alveolar volume (V/VA) and regional lung expansion (FRCR/TLCR) were measured in twelve normal male human subjects in seated, supine, lateral decubitus and prone postures using a gamma camera and inhalation of the radioactive gases 81Krm (half-life 13 sec) and 85Krm (half-life 4.4 h). FRCR/TLCR decreased from superior to inferior in all postures except prone where it was uniform; V/VA increased from superior to inferior except in the prone position where it was uniform. In the horizontal axis FRCR/TLCR and V/VA were uniformly distributed except for cranial to caudal gradients (with lower values caudally) in supine and lateral decubitus postures. In the prone posture V/VA tended to be higher in caudal lung zones.     

Voluntary changes in ventilation distribution in the lateral posture.

To determine whether voluntary changes in the pattern of inspiratory muscle contraction influence topographical distribution of ventilation in the lateral decubitus posture during tidal breathing, we studied 4 normal subjects who breathed either naturally (N) or preferentially with intercostal and accessory muscles (IC), or with enhanced motion of the diaphragm and abdomen (Ab). We performed N2 as well as 133Xe washouts (after equilibration) which were measured at the mouth while recording regional count rates by external scintillation detectors. Ventilation per unit volume (delta V/Vo) in the nondependent lung regions was 0.55 +/- 0.05 (mean +/- 1 SD) and 0.42 +/- 0.02 of that in the dependent regions during natural and sustained Ab breathing, respectively. In contrast, during IC breathing this ratio was 0.99 +/- 0.17. Although N2 washout curves obtained during IC breathing more closely approached a monoexponential than did those from N and Ab runs, a two compartment analysis of washouts at the mouth did not demonstrate significant differences between breathing patterns. We conclude that in the lateral posture voluntary relaxation of the diaphragm during tidal breathing distributes the gas preferentially to the nondependent lung regions. Conversely, during N and Ab breathing the preferential ventilation of dependent regions is due to contraction of the diaphragm.     

Effects of posture on gastro-oesophageal reflux.

Continuous oesophageal pH measurements have been used to assess the influence of posture (lying, sitting, bed-up) on gastro-oesophageal reflux. The percentage of time during which oesophageal pH was below 5 and the number of reflux episodes was significantly reduced when patients were in bed-up position than when sitting or lying. There was no significant difference when sitting and lying positions were compared. The results suggest that by adopting the bed-up position (elevation of the head end of the bed with blocks of 28 cm), the patient will have a symptomatic benefit, the frequency of reflux is decreased, and acid clearing is improved.     

Effects of posture on lung function in obese children

Forced expiratory manoeuvres are recommended performed in sitting posture; however, standing posture has been reported to be usually more advantageous since any diaphragmatic restriction associated with obesity is reduced. Information on the effect of posture on forced expiratory manoeuvres in obese children is lacking. Aim: To determine whether lung function measured in standing compared with sitting posture is increased in overweight and obese children. Methods: One hundred fifteen overweight (n = 23) and obese (n = 92) children (7–17 years old) performed forced expiratory flow‐volume manoeuvres in sitting and standing posture in random order. Results: Forced expiratory volume in 1 s (FEV₁), forced vital capacity (FVC) and forced expiratory flow after 50% of FVC (FEF₅₀) was significantly higher in sitting compared with standing posture [0.8, 1.1 and 2.2 percentage change in absolute values (all with P < 0.05)]. FEV₁/FVC and peak expiratory flow were not significantly different measured in sitting and standing posture; 95%–99% of the variance were explained by differences among individuals (all with P < 0.0001). Conclusions: In conclusion, FEV₁, FVC and FEF₅₀ were all significantly higher when measured in sitting compared with standing posture; however, the improvements were of little clinical significance. These findings confirm that sitting posture is appropriate in obese children when performing forced expiratory flow‐volume manoeuvres. Please cite this paper as: Berntsen B, Edvardsen E, Carlsen K‐H, Kolsgaard MLP and Carlsen KCL. Effects of posture on lung function in obese children. Clin Respir J 2011; 5: 252–257.     

Physiological effects of posture on mask ventilation in awake stable chronic hypercapnic COPD patients.

Stable chronic hypercapnic patients are often prescribed long-term mask noninvasive pressure support ventilation (NPSV). There is a lack of information on the effects of posture on NPSV. Therefore posture induced changes in physiological effects of NPSV in awake stable chronic hypercapnic patients were evaluated. In 12 awake chronic obstructive pulmonary disease (COPD) patients breathing pattern, respiratory muscles, mechanics and dyspnoea (by visual analogue scale: VAS) were evaluated during spontaneous breathing (SB) in sitting posture and during NPSV in sitting, supine and lateral positions randomly assigned. Arterial blood gases were evaluated during SB and at the end of the last NPSV session (whatever the posture). As expected NPSV resulted in a significant improvement in carbon dioxide tension in arterial blood (Pa,CO2) (from 7.4+/-0.85 to 6.9+/-0.7 kPa). When compared with SB, sitting NPSV resulted in a significant increase in tidal volume and minute ventilation and in a significant decrease in breathing frequency. Inspiratory muscle effort as assessed by oesophageal pressure swings and pressure-time product per minute (from 14+/-4.8 to 6.2+/-3.5 cmH2O, and from 240+/-81 to 96+/-60 cmH2O x s x min(-1) respectively), intrinsic dynamic positive end expiratory pressure (from 2.7+/-2.3 to 1.4+/-1.3 cmH2O) and expiratory airway resistance (from 18+/-7 to 5+/-3 cmH2O x L x s(-1)) decreased during sitting NPSV, whereas VAS did not change. Changing posture did not significantly affect any parameter independently of the patients weight, whether obese or not. In awake stable hypercapnic chronic obstructive pulmonary disease patients changing posture does not significantly influence breathing pattern and respiratory muscles during noninvasive pressure support ventilation suggesting that mask ventilation may be performed in different positions without any relevant difference in its effectiveness.     

Topographical ventilation and perfusion distribution during IPPB in the lateral posture.

We measured topographical ventilation and perfusion distribution in the gravity field using 133Xe in 5 normal subjects either during natural breathing or during intermittent positive pressure ventilation (IPPB) in the lateral decubitus posture. The ratio of ventilation of upper regions to that of lower regions increased from 0.61 +/- 0.10 (mean +/- SE) during natural breathing to 0.95 +/- 0.08 during IPPB. In contrast, the ratio of regional perfusion was unchanged in the 2 conditions. Consequently, distribution of regional ventilation-perfusion ratios became less homogeneous during IPPB. Whereas during natural breathing the ratio of ventilation-perfusion of upper regions to that of lower regions was 1.09 +/- 0.18, during IPPB this ratio was 1.52 +/- 0.14. Despite the differences in regional ventilation distribution between natural breathing and IPPB, analysis of multiple-breath 133Xe washouts measured at the mouth did not reveal any difference. The results are consistent with the hypothesis that the magnitude of diaphragmatic tension is the main determinant of topographical ventilation distribution in the lateral posture.     

Effect of posture on ventilation and breathing pattern during room air breathing at rest

We measured minute ventilation (VE), tidal volume (VT), mean inspiratory flow (VT/TI), and occlusion pressure (P.1) in 10 resting subjects breathing room air, in sitting, supine, right and left lateral positions, and compared them with corresponding data on static lung compliance [Cst(l)], dynamic lung compliance [Cdyn(l)], and pulmonary flow resistance [R(l)]. Highest values for VT, VE, VT/TI, P.1, and effective inspiratory impedance [P.1/(VT/Ti)] were observed in the supine posture. Values for P.1 and P.1/(VT/TI in lateral decubitus were intermediate to those obtained when seated and supine. While the increases in P.1 and P.1/(VT/TI) in recumbent postures were qualitatively similar to the decrease in Cdyn(l) and increase in R(l), there was no significant correlation between them, probably reflecting the complex relationship between P.1/(VT/TI) and lung compliance and resistance, as the former, in addition to lung mechanics, also depends on the shape of the inspiratory driving pressure wave, the active inspiratory impedance, the mechanics of the chest wall, and the duration of inspiration.     

Effect of posture on ventilation and breathing pattern during room air breathing at rest

We measured minute ventilation (V_E), tidal volume (V_T), mean inspiratory flow (V_T/T_I), and occlusion pressure (P_.1) in 10 resting subjects breathing room air, in sitting, supine, right and left lateral positions, and compared them with corresponding data on static lung compliance [Cst(l)], dynamic lung compliance [Cdyn(l)], and pulmonary flow resistance [R(l)]. Highest values for V_T, V_E, V_T/T_I, P_.1, and effective inspiratory impedance [P_.1/(V_T/T_i)] were observed in the supine posture. Values for P_.1 and P_.1/(V_T/T_I in lateral decubitus were intermediate to those obtained when seated and supine. While the increases in P_.1 and P_.1/(V_T/T_I) in recumbent postures were qualitatively similar to the decrease in Cdyn(l) and increase in R(l), there was no significant correlation between them, probably reflecting the complex relationship between P_.1/(V_T/T_I) and lung compliance and resistance, as the former, in addition to lung mechanics, also depends on the shape of the inspiratory driving pressure wave, the active inspiratory impedance, the mechanics of the chest wall, and the duration of inspiration. An erratum to this article is available at .     

Effects of upright posture on atrioventricular accessory pathway conduction

The electrophysiologic effects of 45 degrees head-up tilt were studied in 19 patients with atrioventricular accessory pathways. Upright posture enhanced both anterograde and retrograde accessory pathway conduction when compared to the supine position: the anterograde block cycle length decreased from 374 +/- 52 ms (mean +/- standard error) (supine) to 303 +/- 33 ms (tilt) (p less than 0.05); anterograde effective refractory period decreased from 286 +/- 17 to 249 +/- 10 ms (p less than 0.05); retrograde block cycle length shortened from 331 +/- 36 to 291 +/- 35 ms (p less than 0.05); retrograde effective refractory period decreased from 312 +/- 26 ms to 274 +/- 15 ms (p less than 0.05). During induced atrial fibrillation the mean RR interval and the shortest RR interval between preexcited beats decreased approximately 10% with head-up tilt. During orthodromic reciprocating tachycardia, tachycardia cycle length shortened 15%. Tachycardia rate during electrophysiologic study in the head-up position more closely approximated the rate of clinical tachycardia than did the rate in the supine position. Head-up tilt significantly enhances anterograde and retrograde accessory pathway conduction, increases the rate of arrhythmias using an accessory pathway and may be clinically useful in the assessment of patients with an accessory pathway.     

Effects of posture and respiration on body surface electrocardiogram

To define more fully the effects of posture and respiration on electrocardiographic (ECG) patterns, 120-lead body surface potential maps (BSPM) were recorded in 36 normal subjects (aged 21 to 48 years) during cyclic respiration in both supine and upright positions; and at static end-tidal inspiration, functional residual capacity (FRC), total lung capacity (TLC) and residual volume (RV). In addition, BSPMs were recorded at TLC and RV during the Valsalva and Müller maneuvers, respectively. P-wave, QRS and ST-segment time integrals were evaluated. From supine to upright position, there was an inferior torso shift of P-wave and QRS distributions, but no change in amplitude of their maximal or minimal values; ST-segment distributions were spatially unaltered, but there was a significant (p < 0.01) decrease in the maximal value. Relative to maps during cyclic respiration in the upright position, maps at end-tidal respiration were similar; maps at TLC, however, displayed an inferior displacement of P-wave and QRS distributions and a decrease of QRS maximal and minimal values (p < 0.01). Valsalva and Müller maneuvers were not associated with marked changes in the appearances of BSPMs. The magnitude of variability, as assessed by a root-mean-square index, was greatest between maps recorded at TLC and RV; the least variability occurred between maps recorded at end-tidal inspiration and FRC. The variability between maps recorded in the supine and upright positions was intermediate. When root-mean-square variability data of all interventions were normalized by dividing by the respective mean data range (maximum minus minimum) of each time integral, the variability of P wave > ST segment > QRS (p < 0.01).Thus, resting tidal volume respiration has little effect on body surface ECG patterns in normal adults. However, large volume respiration and posture change may substantially alter ECG body surface distributions and should be considered in states involving either factor.     

Negative pressure ventilation. Effects on ventilation during sleep in normal subjects

Negative pressure ventilation (NPV) is used for ventilatory support of patients with respiratory failure due to neuromuscular disorders and thoracic deformities, and to provide ventilatory muscle rest for patients with severe chronic airflow limitation. To determine whether NPV would result in episodes of upper airway obstruction during sleep, we studied five normal subjects on two consecutive nights with the first night serving as a control and NPV being administered on the second night. Ventilators were adjusted so as to reduce the peak phasic diaphragm electromyogram signal by at least 50 percent. All subjects demonstrated an increase in the total number of apneas + hypopneas per hour on NPV control nights. Although differences were not significant, there was a tendency to develop decreased sleep efficiency, sleep fragmentation and altered sleep architecture with NPV. We conclude that nocturnal NPV can induce sleep apneas and impair sleep quality in normal subjects.     

Effects of intermittent negative pressure ventilation on effective ventilation in normal awake subjects

RATIONALE: Previous studies have shown that an increase in inspiratory pressure during nasal intermittent positive pressure ventilation (IPPV) does not result in increased effective minute ventilation (E) due to glottic interference. STUDY OBJECTIVES: To test the consequences of increases in negative pressure ventilation (NPV) on V(E). MATERIAL AND METHODS: Eight healthy awake subjects underwent NPV delivered by an iron lung. First, NPV was started at a respirator frequency (f) of 15 cycles per minute with an inspiratory negative pressure (INP) of - 15 cm H(2)O (F15-P15). Then, f was increased to 20 cycles per minute and INP was kept at - 15 cm H(2)O. Next, f was kept at 20 cycles per minute and INP was reduced to - 30 cm H(2)O (F20-P30). Finally, f was decreased to 15 cycles per minute and INP was kept at - 30 cm H(2)O. At each step and for each breath, effective tidal volume (VT), V(E), and end-tidal carbon dioxide pressure were measured. In three subjects, the glottis width was assessed using fiberoptic bronchoscopy. RESULTS: From spontaneous breathing to the first step of NPV (F15-P15), we observed an inhibition of the phasic inspiratory diaphragmatic electromyogram concomitant to a significant increase in V(E) (p < 0.0005). For the group as a whole, the increase in mechanical ventilation (from F15-P15 to F20-P30) resulted in significant increases in VT and V(E) leading to hypocapnia (p < 0.0005). Moreover, the glottis width did not decrease with the increase in mechanical ventilation. CONCLUSIONS: We conclude that in normal awake subjects, NPV allowed a significant increase in V(E). These results differ from those previously obtained with nasal IPPV in which the glottic width interferes with the delivered mechanical ventilation.     

Effects of posture change on the hemodynamics of the liver

BACKGROUND/AIMS: According to our experience, blood flow in the portal vein may alter according to body posture. It is reported that decreased portal venous flow immediately gives rise to significantly increased blood flow in the hepatic artery. To gain further insight into blood flow changes affected by posture, we examined blood flows in the portal vein, hepatic artery and hepatic vein at different postures. METHODOLOGY: Using a Doppler ultrasound system, the hemodynamics of the portal vein, right hepatic artery, and hepatic vein were examined in 35 patients at supine and left decubitus positions. RESULTS: Portal vein blood flow volumes were significantly lower in the left decubitus position than in the supine. In the right hepatic artery, the left decubitus position gave significantly higher blood flow velocity values than the supine. CONCLUSIONS: Our results indicated that upon change of posture from the supine to left decubitus position, portal vein flow velocity was reduced and hepatic artery flow velocity increased. Changes in portal and hepatic arterial flows by changing posture may be explained by decreased portal flow as a direct result of changed posture, leading to increased hepatic arterial flow to maintain total hepatic blood inflow.     

Effects of spontaneous ventilation on the circulation

Spontaneous inspiration causes an increase in right ventricular stroke volume due to a transient increase in venous return. In contrast, spontaneous inspiration causes a fall in left ventricular stroke volume which is exaggerated in conditions of accentuated pleural pressure swings and pericardial disease. This is manifested by the clinical sign ofpulsus paradoxus. Recent evidence supports the idea thatpulsus paradoxus is the result of two mechanisms. First, negative pleural pressure surrounding the left ventricle is equivalent to an increase in aortic pressure and impedes emptying of the left ventricle much like an increase in afterload. Second, distention of the right ventricle due to the transient increase in venous return causes an elevation of left ventricular diastolic pressure due to ventricular interdependence and therefore impedes left ventricular filling. The mechanism of negative pleural pressure “afterload” is thought to be the major cause of pulsus paradoxus when pleural pressure swings are accentuated. Ventricular interdependence is thought to predominate when pericardial disease is present.     

Effects of posture on sympathetic nervous modulation in patients with chronic heart failure

We investigated which recumbent position is preferred by patients with chronic heart failure (CHF) and whether sympathetic nervous modulation differs in three recumbent positions. We assessed 12 patients with CHF by spectral analysis of heart-rate variability and measurement of plasma norepinephrine concentrations. The right lateral decubitus position was preferred for significantly longer periods than the left lateral decubitus and supine positions. Sympathetic nervous modulation was most attenuated in the right lateral decubitus position. The right lateral decubitus position preferred by patients with CHF may be a self-protective mechanism to control increased sympathetic nervous modulation.