Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0020440 (hypercapnia)
 7,939 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To investigate the response of inspiratory and expiratory muscles to naturally occurring inspiratory resistive loads in the absence of conscious control, five male "snorers" were studied during non-rapid-eye-movement (NREM) sleep with and without continuous positive airway pressure (CPAP). Diaphragm (EMGdi) and scalene (EMGsc) electromyographic activity were monitored with surface electrodes and abdominal EMG activity (EMGab) with wire electrodes. Subjects were studied in the following conditions: 1) awake, 2) stage 2 sleep, 3) stage 3/4 sleep, 4) CPAP during stage 3/4 sleep, 5) CPAP plus end-tidal CO2 pressure (PETCO2) isocapnic to stage 2 sleep, and 6) CPAP plus PETCO2 isocapnic to stage 3/4 sleep. Inspired pulmonary resistance (RL) at peak flow rate and PETCO2 increased in all stages of sleep. Activity of EMGdi, EMGsc, and EMGab increased significantly in stage 3/4 sleep. CPAP reduced RL at peak flow, increased tidal volume and expired ventilation, and reduced PETCO2. EMGdi and EMGsc were reduced, and EMGab was silenced. During CPAP, with CO2 added to make PETCO2 isocapnic to stage 3/4 sleep, EMGsc and EMGab increased, but EMGdi was augmented in only one-half of the trials. EMG activity in this condition, however, was only 75% (EMGsc) and 43% (EMGab) of the activity observed during eupneic breathing in stage 3/4 sleep when PETCO2 was equal but RL was much higher. We conclude that during NREM sleep 1) inspiratory and expiratory muscles respond to internal inspiratory resistive loads and the associated dynamic airway narrowing and turbulent flow developed throughout inspiration, 2) some of the augmentation of respiratory muscle activity is also due to the hypercapnia that accompanies loading, and 3) the abdominal muscles are the most sensitive to load and CO2 and the diaphragm is the least sensitive.
 ...
PMID:Effect of sleep-induced increases in upper airway resistance on respiratory muscle activity. 201 Mar 72

In anesthetized dogs with progressive hypercapnia, the relationships between tidal volume (VT) or occluded inspiratory esophageal pressure swings (Pes) and diaphragm (Edi) or thoracic inspiratory muscle (Etm) peak electrical activity were determined after either cordotomy at C7-T1 or bilateral phrenicotomy, and used together with the Etm vs Edi relationships established in intact and vagotomized dogs to estimate the contribution of each muscle group to VT and Pes observed under the latter conditions. Etm was obtained as the mean of scalene, 2nd and 5th parasternal peak activity, the relationships between these activities being the same under all conditions. In supine and head-up phrenicotomized dogs, VT and Pes increased linearly with Etm and were unaffected by body position. After cordotomy, VT and Pes increased progressively less with increasing Edi and at any Edi were smaller in the head-up posture. Diaphragm relative contribution to VT and Pes was greater when supine than head-up and greater after than before vagotomy, but in all cases it decreased with increasing chemical drive. That of the thoracic inspiratory muscles increased with chemical drive and eventually became equal to (supine) or larger than (head-up) diaphragm contribution.
 ...
PMID:Electrical and mechanical output of the inspiratory muscles in anesthetized dogs. 233 94

Congenital central hypoventilation syndrome was diagnosed in an infant who since birth had shallow respiration and CO2 retention during sleep, absent ventilatory response to hypercarbia, and no underlying disease or trauma to account for the symptoms. Diaphragm pacing was started at the age of 8 1/2 months and has been successfully carried out at home, guided by end-tidal CO2 monitoring. After 22 months of home treatment, at the age of two years 9 months, linear growth and psychomotor development are progressing normally, while previous symptoms of cor pulmonale have not progressed.
 ...
PMID:Congenital central hypoventilation syndrome treated with diaphragm pacing. 660 58

Diaphragm pacing was used for treating 6 infants with congenital hypoventilation syndrome at the Children's Memorial Hospital, Chicago. All patients had inadequate sleep-related ventilation and absent ventilatory response to hypercarbia. A single incision was utilized to implant both the electrode and receiver. The phrenic nerve was isolated with a piece of pericardium to minimize injury. All infants required bilateral nerve pacing to obtain satisfactory ventilation (normal transcutaneous measurements of partial pressure of oxygen and end-tidal pressure of carbon dioxide). The technical details described here are helpful in achieving successful phrenic nerve pacing in infants with results comparable to those reported in adults.
 ...
PMID:Diaphragm pacing in infants and children: report of a simplified technique and review of experience. 677 19

In 7 conscious, unsedated goats with chronically implanted diaphragm electrodes, the effect of respiratory loading on the relationship between occlusion pressure and diaphragm EMG was studied. Diaphragm electrical activity (ED) quantified by the moving average technique was measured in separate trials during progressive hyperoxic hypercapnia and progressive isocapnic hypoxia, both before and after inspiratory resistance had been increased by externally applied loads. Airway occlusion was performed during inspiration on random breaths at functional residual capacity, and the maximum negative pressure (Pmax) was measured. In all 7 goats, occlusion pressure was greater with external loads (EL) than control. The peak ED of unoccluded breaths was greater with EL than control in all animals during hypoxia but in only 3 of the animals during hypercapnia. In half of the trials, the ratio of Pmax to ED of occluded or unoccluded breaths was higher with EL than control. In the remaining studies, the ratio was the same. FRC was unaffected by EL. In the one goat in which it was measured, intercostal EMG was also greater during EL than control. These results suggest that the inspiratory muscles other than the diaphragm are recruited during EL causing the Pmax to ED ratio to rise even if neuromechanical coupling remains unchanged. It is speculated that in conscious, unsedated animals, acute increases in the resistance to air flow affect the distribution of respiratory motor activity.
 ...
PMID:Effect of respiratory loading on the relationship between occlusion pressure and diaphragm EMG during hypoxia and hypercapnia. 683 35

In contrast to adults, newborn infants breathe from an elevated end-expiratory lung volume, determined by the interaction of airflow retardation (braking) by the diaphragm and larynx, and expiratory duration. To determine the effect of hypercapnia on this strategy, we examined changes in respiratory muscle activity and the ventilatory response to CO2 breathing in eight premature infants 33-34 wk gestational age in the first 3 postnatal days. We recorded tidal volume, airflow, and electromyograms (EMG) of the laryngeal abductor [posterior cricoarytenoid (PCA)], which abducts the vocal cords, and diaphragm during behaviorally determined quiet sleep in room air and during steady-state inhalation of 2% CO2 in air. As expected, tidal volume increased (P < 0.0005) without a change in inspiratory duration with hypercapnia. Unexpectedly, in all subjects, expiratory duration was longer during CO2 inhalation (P < 0.001), accompanied by marked changes in expiratory flow patterns consistent with increased expiratory braking. Diaphragm post-inspiratory EMG activity increased with hypercapnia (P < 0.005) with no change in baseline diaphragm or PCA EMG activity. Peak inspiratory EMG activity of the diaphragm and PCA increased with CO2 (10 and 37%, respectively; P < 0.05). We conclude that the mechanisms used to elevate end-expiratory lung volume are enhanced during hypercapnia in premature infants. This breathing strategy may be important in maintaining gas exchange in infants with lung disease.
 ...
PMID:Hypercapnia increases expiratory braking in preterm infants. 812 87

The purpose of this study was to determine the relationship between intrathoracic pressure (delta ITP) and diaphragm shortening (DS) during the development of diaphragm fatigue. Fatigue of the diaphragm was produced by having rats breath 15% CO2 in O2. Diaphragm shortening increased significantly to 178% of control during the first 5 min of hypercapnia and then decreased to 86% of control at approximately 80 min. Twenty minutes after terminating hypercapnia, DS increased to 115% of the prehypercapnic value. delta ITP increased to 199% of control following 5 min of hypercapnia and continued to increase, reaching 267% of control at the end of the hypercapnic period. Twenty minutes later, delta ITP was 147% of control. These results illustrate that during increased respiratory work, DS can decrease while intrathoracic pressure remains increased. These findings suggest that intrathoracic pressure may not always reflect the contractile status of the diaphragm. These findings are consistent with other studies indicating that as the diaphragm fatigues, accessory respiratory muscle activity increases to maintain delta ITP.
 ...
PMID:Diaphragm shortening and intrathoracic pressure during hypercapnia in rats. 951 16

Relatively little is known about the combined effects of hypercapnia and fatigue on the human diaphragm. We examined the effects of acute hypercapnia and fatigue in seven subjects by measuring changes in transdiaphragmatic pressure (Pdi) elicited by cervical magnetic stimulation after 2 min maximal voluntary ventilation (MVV) while breathing air and also with the inspired PCO(2) increased to 8% for 12 min before and during the MVV. Diaphragm strength was assessed before and at 0, 20, 40, 60, and 90 min after the MVV in both studies with the subjects breathing air. There was no difference in the level of ventilation for each run. Mean (+/- SD) twitch Pdi (TwPdi) fell significantly (p < 0.01) at 20 min after the control and hypercapnic MVV; (30.4 [7.8] to 27.0 [8.1] cm H(2)O control and 30.3 [4.1] to 27.3 [5.0] cm H(2)O CO(2)) and remained significantly (p < 0.01) below baseline. The changes in TwPdi at 20 to 90 min were not significantly different between the control and CO(2) runs. The decrease in TwPdi at 0 min after MVV, however, was greater (15%) in the hypercapnic run than in the control run (8.1%) (p < 0.05) when compared with baseline valves. Hypercapnia does not intensify long lasting fatigue but may reduce diaphragm contractility immediately after MVV.
 ...
PMID:Effect of hypercapnia on maximal voluntary ventilation and diaphragm fatigue in normal humans. 1055 22

Diaphragm fatigue may contribute to respiratory failure. (31)P-nuclear magnetic resonance spectroscopy is a useful tool to assess energetic changes within the diaphragm during fatigue, as indicated by P(i) accumulation and phosphocreatine (PCr) depletion. We hypothesized that loaded breathing during hypoxia would lead to diaphragm fatigue and inadequate aerobic metabolism. Seven piglets were anesthetized by using halothane inhalation. Diaphragmatic contractility was assessed by transdiaphragmatic pressure (Pdi) at end expiration with the airway occluded. A nuclear magnetic resonance surface coil placed under the right hemidiaphragm measured P(i) and PCr during four conditions: control, inspiratory resistive breathing (IRB), IRB with hypoxia, and recovery (IRB without hypoxia). IRB alone resulted in hypercarbia (32 +/- 7 to 61 +/- 21 Torr) and respiratory acidosis but no change in diaphragm force output or aerobic metabolism. Combined IRB and hypoxia resulted in decreased force output (Pdi decreased by 40%; from 30 +/- 17 to 19 +/- 11 mmHg) and evidence of metabolic stress (ratio of P(i) to PCr increased by 290%; from 0.19 +/- 0.09 to 0.74 +/- 0.27). We conclude that diaphragm fatigue associated with inadequate aerobic oxidative metabolism occurs in the setting of loaded breathing and hypoxia. Conversely, aerobic metabolism and force output of the diaphragm remain unchanged from control during loaded normoxic or hyperoxic breathing despite the onset of respiratory failure.
 ...
PMID:Effects of loaded breathing and hypoxia on diaphragm metabolism as measured by (31)P-NMR spectroscopy. 1071 Mar 88

The effects of sleep on the ventilatory responses to hypercapnia have been well described in animals and in humans. In contrast, there is little information for genioglossus (GG) responses to a range of CO(2) stimuli across all sleep-wake states. Given the notion that sleep, especially rapid eye movement (REM) sleep, may cause greater suppression of muscles with both respiratory and nonrespiratory functions, this study tests the hypothesis that GG activity will be differentially affected by sleep-wake states with major suppression in REM sleep despite excitation by CO(2). Seven rats were chronically implanted with electroencephalogram, neck, GG, and diaphragm electrodes, and responses to 0, 1, 3, 5, 7, and 9% CO(2) were recorded. Diaphragm activity and respiratory rate increased with CO(2) (P < 0.001) across sleep-wake states with significant increases at 3-5% CO(2) compared with 0% CO(2) controls (P < 0.05). Phasic GG activity also increased in hypercapnia but required higher CO(2) (7-9%) for significant activation (P < 0.05). Further studies in 15 urethane-anesthetized rats with the vagi intact (n = 6) and cut (n = 9) showed that intact vagi delayed GG recruitment with hypercapnia but did not affect diaphragm responses. In the naturally sleeping rats, we also showed that GG activity was significantly reduced in non-REM and REM sleep (P < 0.04) and was almost abolished in REM even with stimulation by 9% CO(2) (decrease = 80.4% vs. wakefulness). Such major suppression of GG activity in REM, even with significant respiratory stimulation, may explain why obstructive apneas are more common in REM sleep.
 ...
PMID:Effects of sleep-wake state on the genioglossus vs.diaphragm muscle response to CO(2) in rats. 1179 3


1 2 Next >>