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Biomedical subjects

G T Ford

Publications and source records attributed to G T Ford.

At least 19 recordsLinked to original sources
PubMed2005

Comparison and reliability of two non-invasive acetylene uptake techniques for the measurement of cardiac output.

Comparison and reliability of two non-invasive acetylene uptake techniques for the measurement of cardiac output. Thirteen trained male cyclists performed CO2 rebreathing (CO2RB) at intensities from rest to 200 W, and open-circuit acetylene uptake (OpCirc) and single-breath acetylene uptake (SB) at intensities from rest to 300 W, with all procedures using 50 W increments. Oxygen consumption VO2 cardiac output Q and heart rate (HR), were measured at each stage, and the values for each variable were compared within each intensity to determine reliability of the measuring device. Both the OpCirc and SBs were shown to be reliable measures of cardiac output (r = 0.95 and 0.92, respectively) with decreasing coefficients of variation (CV) as intensity increased, and were similar to published data. The Q-VO2 relationship using the SB diverged from the regression line for OpCirc and CO2RB. Linear regression of the Q--VO2 relationship for CO2RB was y = 6.18 x VO2 + 2.59 for OpCirc was y = 6.12 x VO2 + 2.98 and for SB was y = 5.05 x VO2 + 3.76. The OpCirc and SBs were both shown to be reliable techniques for measuring cardiac output, comparable to previously reported cardiac output measurements, and suitable for use in exercise testing. However, the SB, requiring a constant, slow exhalation rate, made the procedure difficult to perform at higher exercise intensities.

Acetylene↗
PubMed2001

Effects of vagal denervation on cardiorespiratory and behavioral responses in the newborn lamb.

Recently, Wong et al. (Wong KA, Bano A, Rigaux A, Wang B, Bharadwaj B, Schurch S, Green F, Remmers JE, and Hasan SU, J Appl Physiol 85: 849-859, 1998) demonstrated that fetal lambs that have undergone vagal denervation prenatally do not establish adequate alveolar ventilation shortly after birth. In their study, however, vagal denervation was performed prenatally and the deleterious effects of vagal denervation on breathing patterns and gas exchange could have resulted from the prenatal actions of the neurotomy. To quantify the relative roles of pre- vs. postnatal vagal denervation on control of breathing, we studied 14 newborn lambs; 6 were sham operated, and 8 were vagally denervated below the origin of the recurrent laryngeal nerve. Postoperatively, all denervated animals became hypoxemic and seven of eight succumbed to respiratory failure. In vagally denervated lambs, expiratory time increased, whereas respiratory rate, minute ventilation, and lung compliance decreased compared with the sham-operated animals. In the early postoperative period, the frequency of augmented breaths was lower but gradually increased over time in the denervated vs. sham-operated group. The dynamic functional residual capacity was significantly higher than the passive functional residual capacity among the sham-operated group compared with the denervated group. No significant differences were observed in the prevalence of various sleep states and in the amount of total phospholipids or large- and small-aggregate surfactants between the two groups. We provide new evidence indicating that intrauterine actions of denervation are not required to explain the effects of vagal denervation on postnatal survival. Our data suggest that vagal input is critical in the maintenance of normal breathing patterns, end-expiratory lung volume, and gas exchange during the early neonatal period.

Animals↗
PubMed1995

Interaction between postural and respiratory control of human intercostal muscles.

To study the interaction between postural and respiratory control of intercostal muscles, we used electromyography of intercostal muscles of the lateral chest wall in conscious humans. Bipolar fine-wire electrodes were placed in external and internal intercostal muscles in the midaxillary line of four subjects who sat on a bench and breathed through a pneumotachograph. They were instructed to hold their breath at end expiration, rotate their thorax to the right or left, and then hold the rotation while resuming breathing. Holding a rotation induces steady tonic activity in either internal or external intercostal muscles, depending on the direction of the rotation. The degree of rotation was varied from one run to the next, resulting in varied levels of tonic postural activity. When breathing resumes, internal intercostal muscles have their activity almost completely suppressed with each inspiration independently of whether the tonic postural tone is small or large. External intercostal muscles show inspiratory increases in activity superimposed on the postural tone, which apparently amplifies the effect of respiratory input to their motoneurons.

Adult↗
PubMed1993

Multipatient use of prefilled disposable oxygen humidifiers for up to 30 days: patient safety and cost analysis.

BACKGROUND: Prefilled disposable oxygen humidification units have been shown to decrease the likelihood of contamination when compared to reusable oxygen humidification units. However, prefilled disposable humidifiers are expensive when used for single patients, especially in areas of high turnover, and it is not known whether these units need to be routinely changed before they are empty. The number of patients safely using a prefilled disposable humidifier has not been documented in previously reported work. Are patients at risk of nosocomial infections due to cross-contamination when prefilled disposable oxygen humidifiers are applied to multi-patient use? What are the cost benefits of multiple patient use of prefilled disposable oxygen humidifiers? When local practice or physician preference dictates the use of humidification for low-flow oxygen, these questions need to be answered. METHODS & MATERIALS: Data were collected over two time periods to address changes due to seasonal variations and include area of use, number of patients, and quantitative cultures for aerobic microorganisms (including Legionella). Each disposable humidifier was monitored for a period of 1 month or until only 1 inch of water remained. Costs of using reusable humidifiers and prefilled humidifiers and therapist/nurse time to initiate therapy with both units were compared. During this period, 60 reusable humidifiers were also cultured for aerobic microorganisms and Legionella. RESULTS: We report results on 1,311 of the 1,315 disposable prefilled oxygen humidifiers used. We saw no significant growth in any of the prefilled disposable humidifiers for periods of up to 30 days, with > 100 humidifiers having been used by > 20 patients. CONCLUSIONS: Our results show that prefilled disposable oxygen humidifiers can be used without cross-contamination, on multiple patients, for a period of 1 month. The use of prefilled humidifiers in this way represents a substantial cost saving when compared to reusable humidifiers.

Alberta↗
PubMed1993

Respiratory physiology in upper abdominal surgery.

This article describes the pathophysiology of the respiratory system after upper abdominal surgery, emphasizing the role of respiratory muscle dysfunction. The history of current techniques to measure respiratory muscle function are reviewed. The authors describe the postoperative pattern of breathing, speculate on the physiologic mechanisms responsible and discuss the data supporting the role of reflexes arising from the abdomen and the shift of neural output to different respiratory muscles. Finally, the authors review the impact of "closed" surgical interventions such as laparoscopic cholecystectomy.

Abdomen↗
PubMed1992

Intercostal muscles are used during rotation of the thorax in humans.

To test the idea that the lateral intercostal muscles may be more suited to aid in rotational than respiratory movements of the thorax, we inserted bipolar fine-wire electrodes in external and internal intercostal muscles in the right midaxillary line in nine sitting subjects and examined the pattern of contraction of these muscles during voluntary axial rotations of the thorax (30-35 degrees), resting breathing, and CO2-induced hyperpnea. The right external intercostal muscles were strongly recruited in rotations to the left but were not active in rotations to the right. In contrast, the right internal intercostal muscles were active in rotations to the right but not in rotations to the left. Rotations completed in 1 or 2 s were associated with an early burst of electromyographic activity, followed by a low plateau that persisted while the rotation was held. Rotations made very gradually over 5-10 s were associated with gradually rising electromyographic activity. The amplitude of activity recorded during 30-35 degrees rotations was equivalent to that measured when minute ventilation was increased by CO2 to 50 l/min. We conclude that the lateral intercostal muscles have a major role in producing axial rotations of the thorax.

Adult↗
PubMed1988

Inhibition of breathing associated with gallbladder stimulation in dogs.

The effect of mechanical stimulation of the gallbladder on breathing was studied in anesthetized spontaneously breathing dogs. Measurements of tidal volume, breathing frequency, rib cage and abdominal diameter, transdiaphragmatic pressure, and electrical activity of the diaphragm were made while traction or compression was applied to the gallbladder for periods of 30 s. Both forms of mechanical stimulation produced similar changes, including large decreases in tidal volume, respiratory rate, electrical activity of the diaphragm, and transdiaphragmatic pressure swings. Inspiratory rib cage expansion was little affected, but abdominal expansion was greatly reduced, and swings in gastric pressure were reduced more than swings in pleural pressure, indicating a selective decrease in diaphragmatic activity. Recovery of all measured parameters returned toward control values, despite continued traction or compression. Some inhibition persisted after the stimulus was withdrawn. The very brief interval between stimulus and response suggested that the mechanism was a neural reflex. The afferents involved are unknown but are not purely vagal in nature, since qualitatively similar results were seen in animals after vagotomy. The alteration in breathing frequency indicates that at least part of the reflex is supraspinally mediated. The change in pattern of breathing closely resembles that seen in subjects after abdominal surgery and supports the theory that reflex inhibition of breathing contributes to postoperative pulmonary complications seen in those subjects.

Animals↗
PubMed1987

Effect of lung volume on breath holding.

The mechanism by which large lung volume lessens the discomfort of breath holding and prolongs breath-hold time was studied by analyzing the pressure waves made by diaphragm contractions during breath holds at various lung volumes. Subjects rebreathed a mixture of 8% CO2-92% O2 and commenced breath holding after reaching an alveolar plateau. At all volumes, regular rhythmic contractions of inspiratory muscles, followed by means of gastric and pleural pressures, increased in amplitude and frequency until the breakpoint. Expiratory muscle activity was more prominent in some subjects than others, and increased through each breath hold. Increasing lung volume caused a delay in onset and a decrease in frequency of contractions with no consistent change in duty cycle and a decline in magnitude of esophageal pressure swings that could be accounted for by force-length and geometric properties. The effect of lung volume on the timing of contractions most resembled that of a chest wall reflex and is consistent with the hypothesis that the contractions are a major source of dyspnea in breath holding.

Carbon Dioxide↗
PubMed1984

Diaphragm function and respiratory response after upper abdominal surgery in dogs.

Decreased diaphragm activity has been demonstrated after cholecystectomy in humans (Am. Rev. Respir. Dis. 127: 431-436, 1983). To investigate the mechanism(s) of postoperative diaphragm dysfunction we have established a dog model. Three groups of mongrel dogs were studied under general anesthesia: six dogs received no surgery (control); nine dogs underwent upper abdominal surgery (cholecystectomy); and six dogs underwent lower abdominal surgery (pseudoappendectomy). Diaphragm function was assessed by changes in transdiaphragmatic pressure swings, the ratio of changes in gastric to esophageal pressure swings, and the ratio of changes in abdominal to rib cage diameters during quiet tidal breathing. In the upper abdominal surgery group there were significant postoperative decreases in all parameters of diaphragm function and an increase in minute ventilation and respiratory frequency. However, there were no significant postoperative changes in the parameters of diaphragm function in the control or lower abdominal surgery groups. These studies establish that general anesthesia is not responsible for the reduced diaphragm activity seen postoperatively and that diaphragm function is not affected by lower abdominal surgery in dogs.

Abdomen↗
PubMed1983

Diaphragm function after upper abdominal surgery in humans.

Patients undergoing upper abdominal surgery characteristically develop changes in lung function and are liable to develop atelectasis in the lower lobes. We studied 15 patients to assess lung function and, in particular, diaphragm function in patients undergoing cholecystectomy. Postoperatively, forced expiratory volume in one second and vital capacity decreased in all patients. The alveolar-arterial oxygen difference widened in the 10 patients in whom it was measured. Chest roentgenograms demonstrated patchy atelectasis in 9 of the 10 patients in whom films were obtained. There was a significant reduction in tidal volume with no change in minute ventilation immediately postoperatively. Diaphragm function was assessed by: changes in transdiaphragmatic pressure swings during quiet tidal breathing, the ratio of changes in gastric to esophogeal pressure swings, and the ratio of changes in abdominal to rib cage diameters. The results showed a significant decrease in changes in transdiaphragmatic pressure and the ratio of changes in gastric to esophogeal pressure swings in the postoperative period. In the 4 patients studied with magnetometers, there was a reduction in the ratio of changes in abdominal to rib cage diameters in all patients. These data indicate reduced diaphragm activity in the postoperative period, with a shift from predominantly abdominal to rib cage breathing. There was a reversal toward normal function by 24 h. This reduction in diaphragm function may be responsible for the atelectasis, reduced vital capacity, and hypoxemia in postoperative patients.

Adult↗
PubMed1981

Static lung function in puppies after pneumonectomy.

We performed left pneumonectomy on eight puppies at 9 wk of age; seven littermates underwent a sham operation and functioned as controls. All were studied at 20 wk of age, at which time the remaining lung in the animals with pneumonectomy had the same volume, weight, and surface areas as both lungs of the controls. Total lung capacity (TLC) was the same in controls and postpneumonectomy dogs, but in the latter, the ratio of functional residual capacity to TLC (FRC/TLC) and that of residual volume to TLC (RV/TLC) were larger. Lung pressure-volume curves also differed, postpneumonectomy dogs demonstrating slightly greater recoil at lung volumes below TLC. Therefore, the increased FRC and RV of postpneumonectomy animals could not be ascribed to changes in lung recoil and must have been caused by increased chest wall recoil perhaps related to differences in shape between lung and chest wall. Studies of regional lung function revealed reduced aerated lung in the left hemithorax of the postpneumonectomy dogs and increased FRC/TLC and RV/TLC at the left base. The abnormal distribution of regional volumes did not account entirely for the increase in overall FRC and RV. Comparison of excised lung pressure-volume curves in those measured in intact animals revealed better agreement in postpneumonectomy dogs than in controls.

Animals↗
PubMed1981

Shape and regional volume in immersed lung lobes.

We froze 10 isolated canine lower lobes by immersing them in chlorothene (sp gr 1.4) at -20 degrees C. In six instances the contralateral lower lobe was frozen over dry ice. The lobes were then sliced horizontally, and the volume and weight of each slice were measured so that expansion (specific volume) and the amount of tissue (weight) could be assessed as a function of distance down the lung. Lobes frozen under chlorothene at low [35% total lung capacity (TLC)] and medium [60% TLC] volumes demonstrated a gradient of regional expansion that was about half that predicted on the basis of pleural surface pressure. Lobes frozen under chlorothene at high volumes [80% TLC] did not demonstrate a significant gradient of regional expansion. These results demonstrated tissue interdependence. When lobes frozen under chlorothene were compared with contralateral lobes frozen over dry ice, substantial differences in shape were evident. Chlorothene-frozen lobes had greater vertical height, and a smaller fraction of their weight was present in dependent regions: lobes frozen in chlorothene had half as much tissue over the lower 40% of their vertical height as did lobes frozen over dry ice. We demonstrated two mechanisms by which relative homogeneity of regional expansion was maintained in response to differences in pleural pressure, tissue interdependence and tissue movement from more compressed to less compressed regions.

Air Pressure↗
PubMed1980

Forces involved in lobar atelectasis in intact dogs.

When an excised lung lobe undergoes atelectasis, its shape differs from that observed when lobar atelectasis occurs in an intact animal: the chest wall deforms the collapsing lobe. In eight anesthetized dogs in the left lateral position we measured lung volume and transpulmonary pressure during the development of atelectasis. We then induced atelectasis of the left lower lobe with the rest of the lung maintained at FRC and measured lobar volume and "translobar" (lobar minus esophageal) pressure. Lung and lobar volumes were measured by prebreathing the animal with 88% O2-12% N2, occluding the airway and observing the increase in lung or lobar N2 concentration. When the left lower lobe alone collapsed, translobar pressures were more negative than transpulmonary pressure at the same relative volume when the whole lung collapsed. This pressure difference, which represents the deforming force applied to the lobe minus the pressure costs of deformation, averaged 3 cmH2O at 50% FRC. Infusion of 25 ml of normal saline into the pleural space sharply reduced the difference pulmonary pressure during lung collapse: this difference was abolished at 80% FRC and halved at 50% FRC. The large effect of the small volume of fluid suggested that deforming forces were largely generated in relatively local areas, such as regions of the chest wall with sharp angulation.

Animals↗
PubMed1979

Volume shifts with partial submersion of isolated lung lobes.

When an isolated lung lobe is partially submerged, volume moves from the submerged part to the unsubmerged part. We partially submerged isolated dog lobes of known weight and volume, and measured airway pressure and, by water displacement, the volume of the submerged part. The lobe was then air-dried and sectioned at the waterline and each part weighed. Multiplying lobar volume by the fractional weight of the submerged part yielded the volume of the submerged part before immersion, and therefore the volume shift to the unsubmerged part due to immersion. Dividing this volume shift by the immersion-induced change in airway pressure gave the compliance (Cr') of the unsubmerged part. Cr' was compared to Cr, the compliance of the unsubmerged part when it was inflated with air. Cr/Cr' was linearly related to the degree of immersion: as immersion increased Cr/Cr' fell; so when lobes were 80% immersed Cr/Cr' was 0.3--0.5, indicating that compressing the lower part of the lung made the upper easier to expand. This behavior could be explained if with immersion lung units moved from the submerged part to the unsubmerged part and this shift increased with the degree of immersion. We demonstrated that when one part of a lobe was compressed lung units moved away from the compressive force and that this movement could occur without similar movement of the pleural surace. Tissue movement probably accounted at least in part for our results.

Animals↗