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Biomedical subjects

G D Swanson

Publications and source records attributed to G D Swanson.

71 records · Page 4Linked to original sources
PubMed1979

Overview of ventilatory control during exercise.

Practically every respiratory physiologist of the last 100 years has studied the ventilatory response to exercise. Yet we still do not know the cause of increased ventilation associated with exercise. This overview considers the problem from a broad observational point of view. Data from studies combining exercise with continuous inspired CO2 and "slug" CO2 breathing imply a feed-forward/feed-back structure for the ventilatory controller. The feed-forward stimulus is correlated to CO2 production. Feed-back senses arterial CO2 tension and acts to minimize the effects of correlation errors and correlation slope errors in the feed-forward path. This feed-forward/feed-back structure yields a regulated arterial CO2 and a tight coupling of ventilation to CO2 production. The feed-back mechanism acts via the carotid body, and indirectly via the central chemoreceptor. A variety of mechanisms are discussed that may be involved in providing the feed-forward stimulus. In particular, the intravenous loading experimental results are considered in terms of an appropriate feed-forward stimulus.

Animals↗
PubMed1978

Effect of hypercapnia on hypoxic ventilatory drive in carotid body-resected man.

Steplike end-tidal hypoxic drives (PETCO2 = 53 Torr) lasting for 5 min were generated in a group of normal subjects and a group of carotid body-resected subjects when end-tidal CO2 was maintained constant under eucapnic (PETCO2 = 39 Torr) and hypercapnic (PETCO2 = 49 Torr) conditions. The hypoxic ventilatory response of the normal subjects was prompt and significant in eucapnia and was enhanced in the hypercapnic state, evidencing CO2-O2 interaction. In contrast, the carotid body-resected subjects did not respond to eucapnic hypoxia but did demonstrate a small but significant ventilatory response to hypoxia against the hypercapnic background. This suggests that the aortic bodies in man may contribute a small component of the hypoxic ventilatory drive under hypercapnic conditions, although the possibility of neuromalike ending regeneration cannot be excluded.

Adult↗
PubMed1977

Evaluation of the Grodins respiratory model via dynamic end-tidal forcing.

The Grodins model for respiratory physiology is very descriptive in simulating the lung-blood-tissue gas transport and exchange system, including detail not found in previous or more recent models. Three alternative controllers have been proposed for control of this gas exchange system. This paper indicates how dynamic endtidal forcing enhances behavioral differences among these three controllers and therefore enhances discrimination when the behavior is compared with subject data. Previously published end-tidal forcing data are used in the comparison. Several deficiencies in the controllers for the Grodins model are indicated.

Carbon Dioxide↗
PubMed1976

Posthyperventilation isocapnic hyperpnea.

Subjects voluntarily hyperventilated for 10 breaths. A dynamic end-tidal forcing technique manipulated inspired gases to hold end-tidal CO2-O2 tensions at normal values during the voluntary ventilation period and the postvoluntary ventilation recovery period when the subjects returned to spontaneous breathing. Six of the seven subjects studied exhibited a hyperpnea during the recovery period. Although intersubject and intrasubject variations were evident, the average response for 30 experiments in the six subjects was characterized by an initial drop to 32% of the hyperventilation magnitude followed by an exponential-like decrease with a time constant of 22 s. This recovery period response is consistent with theoretical properties of neural network and physical oscillators where there is a persistence in the amplitude response after the removal of the stimulus. Thus, such oscillator properties may govern the respiratory center behavior in man. Furthermore, since isocapnic voluntary ventilation increases cardiac output, the recovery period response may be a consequence of cardiodynamic hyperpnea.

Adult↗
PubMed1976

New electronics for the Beckman LB-1 carbon dioxide analyzer.

This paper describes an amplifier and linearizer for the Beckman LB-1 carbon dioxide analyzer head. All electronics are solid state and DC regulated in contrast to the original LB-1 amplifier which was of vacuum tube design and AC regulated largely by means of a voltage stabilizer transformer. A new detection principle is adopted which reduces drift due to mechanical imperfections of the chopper motor (e.g., bearing drag), but also offers the advantage that the phasing of the chopper blades is no longer necessary. Furthermore, the amplifier with a digital readout and an end-tidal hold circuit can be built for less than $500 and is plug compatible with the LB-1 head.

Carbon Dioxide↗
PubMed1975

Respiratory effects of delta-9-tetrahydrocannabinol.

The respiratory effects of smoked marijuana and oral delta-9-tetrahydrocannabinol (delta9THC) have been studied in healthy males by assessing displacement of the respiratory response curve. Both cause slight respiratory depression, in some subjects it stimulates respiration. High doses of pentobarbital depress respiration but low doses apparently do not.

Administration, Oral↗
PubMed1975

Step changes in end-tidal CO2: methods and implications.

A dynamic end-tidal forcing technique for producing step changes in end-tidal CO2 with end-tidal O2 held constant independent of the ventilation response or the mixed venous return is introduced for characterizing the human ventilation response to end-tidal CO2 step changes for both normoxic (PAO2 = 125 Torr) and hypoxic (PAO2 = 60 Torr) conditions. The ventilation response approaches a steady state within 5 min. In normoxia, the on-transient is faster than the off-transient, presumably reflecting the action of cerebral blood flow. The hypoxic step response is faster than the normoxic response presumably reflecting the increased contribution from the carotid body. The delay in the ventilation response after the change in end-tidal CO2 is less in hypoxia than in normoxia and reflects the action of a transport delay and that of a virtual delay. These delays are interpreted with respect to the high-frequency phase shift data for the same subject, generated using sinusoidal end-tidal forcing. The methods of others for experiments utilizing step changes in inspired CO2 are considered with respect to our methods.

Adult↗
PubMedDate not supplied

Silicone implant arthroplasty of the great toe. A review of single stem and flexible hinge implants.

One hundred sixty-five feet were reconstructed with the single stem silicone implant, including patients with hallux regidus, hallux valgus due to degenerative and osteoarthritic joint changes, hallux valgus secondary to rheumatoid arthritis and patients with previous unsuccessful "bunion" procedures. Preoperative pain and intolerance to shoe wear were relieved in the great majority of patients. The amount of correction of the hallux valgus angle was directly related to the preoperative deformity. Infection occurred in 2 patients, and inflammatory reaction to the implant occurred in one patient. One hundred five feet were reconstructed with a flexible hinge implant; 94 of the feet had joints destroyed by rheumatoid arthritis. Dramatic improvement in the hallux valgus angle resulted in these feet which had relatively severe preoperative deformities. No implant fractures were recorded. The present survey of our cases, and experiences reported by others, encourage the use of these implants by surgeons who follow the suggested indications, surgical technique, and follow up care.

Adolescent↗