Thoracoabdominal motion during progressive isocapnic hypoxia in conscious man

Nasal airflow and thoracoabdominal motion in children using infrared thermographic video processing

The assessment of apnea and asynchronous breathing requires the application of a facemask connected to a pneumotachograph and inductive transducer bands placed around the chest wall. These contact devices may alter the breathing pattern and are difficult to implement, especially in infants and children. This study validates a contactless image-processing system that simultaneously retrieves breath-related thermal variations from nasal, ribcage, and abdomen regions of interest (ROI) from infrared thermographic video recordings of children. Thermographic videos were obtained in 17 supine, spontaneously breathing unsedated children (0.33-13.75 years), including 8 patients with respiratory pathology. Representative thermographic signals were obtained from each ROI on a frame-by-frame basis. Cronbach's Alpha reliability coefficient assessed the correlation between control nasal pressure period, the visually scored respiratory rate and the fundamental period in the frequency domain of thermographic signals. A cross-correlation function calculated the time delay and the phase angle between ribcage and abdomen variability. A Cronbach's Alpha value of 0.976 (0.992-0.944 95% CI) suggests a small-scale measurement error between thermographic and control periods. The ribcage-abdomen time delay in children with respiratory disease (-0.42 ± 0.707 sec) significantly differed from healthy children (0.22 ± 0.426 sec, P = 0.0125). This novel system reliably acquired time-aligned nasal airflow and thoracoabdominal motion estimates without relying on attached sensor performance and detected asynchronous breathing in pediatric patients.

Influence of body position on pressure and airflow generation during hypoxia and hypercapnia in man

1. Inspiratory oesophageal pressure and ventilatory responses to hyperoxic, progressive hypercapnic rebreathing (HCVR) and isocapnic, progressive hypoxic rebreathing (HVR) were studied in five normal males in both supine and upright seated positions. 2. No significant differences were found in the ventilatory response to hypercapnia between the supine and upright position. The slopes of the relationship between minute ventilation (VI) and the increase of end tidal PCO2 (delta P(ET), CO2) were 3.27 +/- 0.23 and 2.76 +/- 0.24 1 min-1 mmHg-1 supine and upright, respectively. However, the change in oesophageal pressure from the end expiratory level observed during quiet breathing to that at peak inspiration (delta P(oes), I) in relationship to delta P(ET),CO2 was greater supine than upright (1.23 +/- 0.07 versus 0.79 +/- 0.11 cmH2O mmHg-1, P < 0.01). 3. In contrast, during hypoxia-stimulated breathing the slope of the minute ventilation versus oxyhaemoglobin saturation curve (VI-Sa,O2) was flatter supine than upright (1.00 +/- 0.03 versus 1.75 +/- 0.05 l min-1 (percentage fall in Sa,O2)-1, P < 0.0001), but delta P(oes), I in relation to Sa,O2 during hypoxic rebreathing was similar supine and upright (0.38 +/- 0.03 versus 0.40 +/- 0.04 cmH2O (percentage fall in Sa,O2)-1, respectively. 4. It is concluded that body position does not affect the ventilatory response to progressive hyperoxic hypercapnia but does affect the relationship between delta P(oes), I and delta P(ET),CO2. In contrast, body position affects the ventilatory response to isocapnic progressive hypoxia, but does not affect the relationship between delta P(oes), I and Sa,O2.

Low-dose sufentanil and lidocaine supplementation of general anaesthesia

This randomized double-blind study compared the effects of: (1) saline infusion (C); (2) sufentanil alone (1.0 micrograms.kg-1) (S); and (3) low-dose sufentanil (0.5 micrograms.kg-1) in combination with lidocaine (1.5 mg.kg-1) (LS): on the cardiovascular responses to tracheal intubation and on postoperative ventilation as monitored by respiratory inductive plethysmography in day-care surgical procedures of approximately 60 min duration. Thirty healthy, unpremedicated patients were studied. Thiopentone requirements were reduced by 40 and 28 per cent in the S and LS groups respectively compared with control (P less than 0.001). Both treatments suppressed HR and BP responses (P less than 0.005) to intubation. Postoperatively, PaCO2 was elevated (P less than 0.05) in group S. Dose-related respiratory depression was observed. The incidence of postoperative apnoea was significantly higher in both S and LS groups than compared with control (P less than 0.05). However, only patients in group S showed higher apnoea index and mean apnoea duration over the initial 10-20 min after surgery compared with control (P less than 0.005). In addition, group S showed slower respiratory frequency and prolonged expiratory time (P less than 0.005). In conclusion, an induction dose of sufentanil (1 microgram.kg-1) used in balanced anaesthesia of less than 70 min duration was associated with significant respiratory depression, particularly during the initial 10-20 min after surgery, whereas low-dose sufentanil (0.5 micrograms.kg-1) with lidocaine (1.5 mg.kg-1) had minimal postoperative respiratory depression and comparable attenuation of pressor responses to intubation.

Cardiovascular response to acute airway obstruction and hypoxia

We wished to evaluate the role of hypoxia in the production of cardiovascular manifestations of acute airway obstruction. We monitored blood pressure, electrocardiogram, and radionuclide ejection fraction in 14 healthy volunteers on exposure to four experimental conditions: expiratory resistive loading while breathing room air (RAL), expiratory resistive loading while hypoxic (HL), hypoxia alone (H), and expiratory resistive loading while voluntarily hyperventilating in a pattern similar to HL trials (VL). Mean respiratory-related oscillation in systolic blood pressure (pulsus paradoxus) increased significantly under each experimental condition compared with those at baseline (2 +/- 2.3 mm Hg): for RAL, 21 +/- 8.4 mm Hg; for HL, 34 +/- 16.3 mm Hg; for H, 10 +/- 5.4 mm Hg; for VL 26 +/- 13.4 mm Hg. Pulsus paradoxus was significantly greater under conditions of moderate hypoxia (saturation, 80%) than of mild hypoxia (saturation, 90%). Electrocardiographic changes were more marked under HL and H conditions than under RAL and VL conditions. HL induced changes in blood pressure and frontal QRS axis that were qualitatively similar to those seen in naturally occurring asthma. Radionuclide ejection fraction showed no dramatic change with any experimental condition. We conclude that hypoxia magnifies the cardiovascular changes induced by acute expiratory resistive loads and may contribute to the degree of pulsus paradoxus seen in severe asthma.

Effect of posture on ventilatory response to steady-state hypoxia and hypercapnia

The ventilatory response to steady-state normocapnic hypoxia and hypercapnia was measured in eight normal subjects after 15 min inhalation of 10.5% oxygen (with added CO2) or 4.2% CO2 in air through a loose-fitting high-flow Venturi mask. The erect (sitting) and the supine postures were studied. Ventilation was measured with inductance coils around the chest and the abdomen (Respitrace). Oxygen saturation was measured with an ear oximeter and PCO2 was measured transcutaneously on forearm skin using a modified pH electrode (Radiometer). In the erect posture (without stimulation), compared to supine, VE(21%) and VT/TI(32%) were greater but TI(19%) and TE(8%), abdominal contribution to tidal volume (24%) and 'arterial' PCO2 (0.6 mm Hg) were less. The mean ventilatory response to hypoxia at an 'arterial' PCO2 of 41 +/- 4 mm Hg (SD) was 0.61 +/- 0.34 L X min-1 X Sa-1O2 erect and 0.84 +/- 0.58 supine and to hypercapnia 2.89 +/- 1.4 L X min-1 X mm Hg-1 erect and 3.73 +/- 2.35 supine. The postural differences did not reach statistical significance. The pattern of response to both stimuli was similar, with doubling of VT, constant TI and slight shortening of TE. The abdominal contribution to tidal volume decreased by 9% with both forms of stimulation. In the steady state, the response to peripheral and central chemoreceptor stimuli was identical and essentially independent of position.