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Query: UMLS:C0020440 (hypercapnia)
 7,939 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study examined the relationship between tracheal slowly adapting stretch receptor discharge and smooth muscle activity in a preparation in which the efferent supply to the airway was essentially intact. In 7 anesthetized, paralyzed, artificially ventilated dogs, smooth muscle activity was assessed by measuring the pressure of a water-filled cuff placed in the extrathoracic trachea and action potentials originating from 19 extrathoracic tracheal stretch receptors were recorded from the superior laryngeal nerve. Challenges were: hypercapnia (FI = 0.05 and FI = 0.10), hypoxia (FI = 0.10 and FI = 0.05) and asphyxia. Concurrent increases in cuff pressure and receptor discharge were present in 18 of the endings studied in response to all the challenges presented. The remaining receptor increased its rate of discharge with 10% CO2 and asphyxia; neither receptor discharge or cuff pressure increased with 5% CO2 and hypoxia. Following block of the recurrent laryngeal nerves, baseline values of both cuff pressure and receptor discharge, as well as the responses to asphyxia, decreased; any residual response was eliminated by atropine. Of the 17 receptors whose location could be precisely ascertained, 14 were found in the proximal third of the extrathoracic trachea, and the remaining 3 in the middle third. The temperature at which the nervous conduction was blocked was determined for 3 slowly adapting receptors; it ranged from 4.5 to 12.5 degrees C. Of 5 extrathoracic tracheal rapidly adapting receptors encountered during the course of the experiments, 3 were tested with asphyxia and found to be unaffected. This study shows that tracheal slowly adapting stretch receptors are activated by smooth muscle contractions reflexly induced by chemoreceptor stimulation.
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PMID:Contraction of trachealis muscle and activity of tracheal stretch receptors. 337 5

Patients with breathlessness commonly describe subjective relief when seated near an open window or in front of a fan. Previous studies suggest that a flow of air or application of cold solutions to the face, nasal mucosa, or pharynx may alter ventilation. We hypothesized that a flow of cold air directed against the cheek would reduce the sensation of breathlessness associated with loaded breathing. Sixteen subjects breathed on a device with an inspiratory resistive load (63 cm H2O/L/s) while PCO2 was maintained at 55 torr for 5 min. All studies were performed 4 times with each subject, twice with cold air directed against the cheek (4 degrees to 10 degrees C, 4 km/h) and twice with no flow on the subject. Subjects were asked to rate their breathlessness using a modified Borg scale. Cold air directed on the face reduced breathlessness induced by an inspiratory resistive load and hypercapnia (6.2 +/- 1.7 Borg scale units with no flow, 5.1 +/- 1.7 with cold air; p less than 0.002) without causing a significant reduction in ventilation. This effect was not observed when cold air was directed to the leg and does not appear to be associated with a reduction in the ventilatory response to hypercapnia or with initiation of the diving reflex. We conclude that cold air directed against the cheek significantly reduces dyspnea associated with the combination of hypercapnia and an inspiratory resistive load.
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PMID:Cold facial stimulation reduces breathlessness induced in normal subjects. 360 41

The extracellular pH regulation was studied in the crayfish Astacus leptodactylus (a night animal) as a function of circadian rhythm. The venous acid-base balance (ABB) was determined in the morning (10 a.m.-12 a.m.) and in the evening (10 p.m.-12 p.m.) at PO2 ranging from 29 to 6 kPa and constant ABB in the water at 13 degrees C. In the morning the venous pH (pHv) was maintained constant by metabolic means independently of PO2 from 29 to 10 kPa. In the evening pHv again was constant and independent of PO2 but it was more alkaline by 0.1 unit corresponding to a shift along the in vitro buffer line. At that time, the ventilation required for providing a unit quantity of O2 (i.e. the ventilatory requirement) increased more than for simply providing O2. The related circadian changes of sensitivity of the ventilatory control system were assessed by comparing morning and evening ventilatory responses to 1-h periods of hypoxia and then hypercapnia. In the evening, the amplitude of the responses to both O2 and CO2 increased but the increase in CO2 sensitivity was proportionally more important. This is consistent with the increase of ventilatory requirement and the related decrease of hemolymph PCO2 during this period. It is concluded that in this animal there exists a circadian rhythm of extracellular pH that is achieved by controlling the CO2 partial pressure in the hemolymph. Results are discussed in terms of O2 transport processes and metabolic modulation through pH adjustments.
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PMID:Circadian rhythm of extracellular pH in crayfish at different levels of oxygenation. 365 3

A case is presented which describes a patient who developed hypercarbia resulting from a defective humidifier. A Puritan-Bennett Cascade I humidifier was incorporated into a circle system between the inspiratory dome one way valve and the patient. A screw which supports the thermal well to the head of the humidifier was missing, thereby allowing an intermittent leak to develop in the system. The leak was present when the system pressure dropped to ambient level; however, at positive system pressure the leak sealed. This allowed exhaled gases into the inspiratory limb of the circuit unchecked by the inspiratory valve yet when the breathing circuit was occluded at the patient end and submitted to pressures of 20 and 40 cm H2O, no leaks were detected. Intraoperatively, PaCO2 was noted to be as high as 68 mmHg just prior to removing the humidifier from the circuit and corrected to 38 mmHg within 15 minutes of removal of the humidifier.
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PMID:Carbon dioxide retention associated with a humidifier defect. 366 21

Acute physiological responses to the "PO2-Aerobic Exerciser" (AE), a partial rebreathing device designed to stimulate training at altitudes, were studied in seven healthy men [mean VO2max = 56.1 +@- 10.1 (SD) ml X kg-1 X min-1] who performed cycle ergometer exercise to exhaustion in three experimental situations: a control test (C) breathing normal atmosphere: a test with the device (AE); and a test with the AE air supplemented with oxygen (AEO2'). Arterial oxygen saturation at rest for C, AE, and AEO2' studies was 97 +/- 1, 95 +/- 2, and 97 +/- 1%, respectively (P less than 0.05 for C vs AE and AE vs AEO2'), while at exhaustion it was 95 +/- 1, 87 +/- 2, and 95 +/- 1%, respectively (P less than 0.05 for C vs AE and AE vs AEO2'). Maximum work rate decreased from a control value of 1738 +/- 184 kg X min-1 to 1371 +/- 147 kg X min-1 during AE and remained below control levels during AEO2'; 1554 +/- 110 kg X min-1 (P less than 0.05). Beyond 60% of maximum work rate during AE, inspired CO2 increased to 0.026 +/- 0.005. Mouth pressure swings of up to -19.2 +/- 10.2 and 12.7 +/- 5.7 cm H2O were recorded during AE. While the PO2 aerobic exerciser induced a hypoxic stress, the pertubation imposed was not explained fully by arterial oxygen desaturation. Other factors such as hypercapnia and a flow resistive increase in the work of breathing appear to have influenced work capacity during the use of the device.
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PMID:Influence of supplemental oxygen on the physiological response to the PO2 aerobic exerciser. 370 49

We studied the effect of systemic hypoxemia and hypercarbia on the bronchial blood flow in open-chested, anesthetized dogs. The pulmonary artery and vein of the left lower lobe (LLL) were isolated with cannulas and connected to reservoirs set at atmospheric pressure relative to the base of the LLL. That fraction of the bronchial arterial flow (Qbr) to the LLL, which flowed through the bronchopulmonary anastomoses into these reservoirs, was continuously measured. The LLL was inflated continuously with 6% CO2 and air at a constant alveolar pressure of 10 cm H2O. Systemic arterial O2 tension (PaO2) and arterial CO2 tension (PaCO2) were varied by separately ventilating the right lung through a bifurcated endotracheal tube. A 10-min period was allowed for stabilization after each change in experimental condition. Anastomotic Qbr was measured for 5 min during each experiment. In separate animals, similar studies were performed before and 30 min after intravenously administered indomethacin (6 mg/kg body weight). During normoxic conditions when PaO2 was 79 +/- 8 torr (mean +/- SEM), the mean anastomotic Qbr was 5.7 +/- 2.0 ml/min (n = 9). This flow increased to 8.3 +/- 2.5 ml/min (p less than 0.05) during hypoxemic conditions (PaO2, 38 +/- 3). The anastomotic Qbr increased from 5.8 +/- 1 to 9.0 +/- 2 ml/min (p less than 0.005) when PaCO2 was increased from 23 +/- 1 to 47 +/- 2 torr (n = 11). Pretreatment with intravenously administered indomethacin blocked both the hypoxemia-induced (n = 4) and hypercarbia-induced (n = 4) increases in anastomotic Qbr. We conclude that both hypoxemia and hypercarbia increased the anastomotic Qbr through a mechanism involving cyclooxygenase products of arachidonic acid.
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PMID:Hypoxia and hypercarbia increase bronchial blood flow through bronchopulmonary anastomoses in anesthetized dogs. 372 66

A dual-label radioisotope method to measure regional cerebral blood flow (CBF) with [14C]butanol and the single-transit brain extraction of [3H]water (Ew) was modified to permit concomittant measurement of the exit time through the cerebrovasculature of a bolus (BET) of 51chromium (51Cr)-labeled ethylenediaminetetraacetic acid (EDTA) in rodents. First, [51Cr]EDTA was injected intravenously via the femoral vein and its transit through cerebrovasculature determined by external gamma counting. The BET measurement was then used to determine the optimum time for animal sacrifice for subsequent measurement of CBF and Ew to minimize both intravascular contamination and washout of butanol and water. This procedure resulted in higher CBF at moderate hypercapnia and slightly lower Ew as a function of arterial CO2 content than previously found using a fixed interval for sacrifice.
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PMID:A modified method for the simultaneous determination of regional single-transit brain extraction of diffusion-limited compounds and cerebral blood flow: utilization of non-invasive measurement of transit time. 392 42

Respiratory muscle weakness is considered to be a factor in the inability to wean from mechanical ventilation. To assess this possibility, the present study examined the mechanical behavior of the diaphragm by measuring the change in transdiaphragmatic pressure (delta Pdi) during weaning. Nine "T-piece" weanings were carried out in seven patients with prior weaning failure and were terminated with the development of hypercapnia, hypoxemia, or severe tachypnea. Serial measurements of delta Pdi during these weans revealed that (1) in no case was there a decrease in delta Pdi at termination of weaning, and (2) in the subgroup of patients whose weaning failed because of hypercapnia, the increase in arterial carbon dioxide tension (mean increase of 12 mm Hg) was associated with a significant increase in delta Pdi, from the beginning (21.1 +/- 12.1 cm H2O) to the end (24.8 +/- 13.4 cm H2O) of the trial (p less than 0.05). We conclude that failure to wean in these patients, in particular the development of carbon dioxide retention, was not due to failure of the diaphragm as a pressure generator.
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PMID:Diaphragmatic strength during weaning from mechanical ventilation. 393 89

The purpose of this investigation was to examine the effects of norepinephrine cardiomyopathy (NE-CM) on left ventricular (LV) performance in diabetic rabbits. Diabetes mellitus was produced in 11 rabbits by giving them alloxan monohydrate, 120 mg/kg. Cardiomyopathy was produced in five animals by a 90-min infusion of norepinephrine (2 micrograms/min/kg). Left ventricular contractility and pump function (VF) were examined 2 days later. The effects of hypercapnia and inotropic responsiveness to NE were also determined. VF was assessed by means of left ventricular function curves obtained with constant mean aortic pressure and heart rate and quantified by determining stroke volume (SV) at a left ventricular pressure of 10 cm H2O (SV10). Mean SV10 was 1.22 +/- 0.08 ml in control diabetics but averaged only 0.95 +/- 0.08 ml in diabetics with NE-CM (P less than 0.05). NE-CM markedly reduced LV dP/dt max responses to NE infusion but the increments in SV10 did not differ. Hypercapnia caused significantly greater ventricular depression in NE-CM than in control diabetic rabbits (P less than 0.001). The depressive effect of hypercapnia can be countered in part by the administration of NE in both groups, but differential depression in VF to hypercapnia was persistent between the two groups.
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PMID:Ventricular performance in diabetic rabbits with norepinephrine cardiomyopathy. 394 45

An estimate of the total mass of bone in the Channel catfish Ictalurus punctatus Rafinesque, was obtained by dissection. The wet weight of bone constituted 16.3 +/- 1.9% (+/- S.D.) of the total (live) wet weight, and 25.0 +/- 2.1% of the dry weight. Of the dry skeletal material, 66.3 +/- 11.1% was soluble in strong acid. The acid-soluble material was about half mineral salts, consisting of 19.5 +/- 2.21% Ca2+ and 27.6 +/- 3.22% PO4(3-), with minor fractions of Mg2+ (0.33%) and CO3(2-) (1.67%). The pH values of fluid compartments associated with skull and vertebral bone tissues were 7.420 +/- 0.026 and 7.444 +/- 0.017 (+/- S.E.), respectively, at a normocapnic plasma pH of 7.868 +/- 0.020. In response to external hypercapnia (7.5 Torr), the blood response consisted of an immediate decrease in pH, and a subsequent compensatory rise in both pH and [HCO3-]. This compensatory phase was accompanied by a net apparent H+ excretion to the water. The participation of the mineral salts of the bone compartment in compensation appeared to be negligible, since there was no significant change in either blood [Ca2+] or [PO4(3-)], nor any significant increase in calcium efflux to the water. The intracellular pH values of the bone compartments were only slightly higher than other tissues, and the changes in pHi during hypercapnia were similar in bone and white muscle. Thus, the bone compartment in the fish appears to be well regulated, relatively refractory to acute acid-base disturbance, and does not serve as an ion source during acid-base compensation.
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PMID:The bone compartment in a teleost fish, Ictalurus punctatus: size, composition and acid-base response to hypercapnia. 406


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