Biomedical subjects

A B Adams

Publications and source records attributed to A B Adams.

At least 37 records · Page 2Linked to original sources

PubMed2000

Effects of respiratory impedance on the performance of bi-level pressure ventilators.

BACKGROUND: Noninvasive positive pressure ventilation (NPPV) has been studied in several settings and shown to reduce patient morbidity associated with endotracheal intubation. Intolerance to NPPV has been estimated at 25-33%, a substantial proportion of attempts to ventilate noninvasively. Bi-level pressure ventilators (BPVs) have been designed for NPPV, yet their response to changes in respiratory impedance has not been extensively evaluated. To determine responses of BPVs to changing impedance conditions, we tested 4 BPVs to evaluate the potential for intolerance. We also developed a mathematical model for BPV performance that accounted for impedance conditions, leak, pressure settings, and inspiratory flow cutoff level. METHODS: Four BPV models at the same settings were challenged to ventilate a triggered test lung under a range of impedance conditions while measuring tidal volume (VT) and intrinsic positive end-expiratory pressure (auto-PEEP). The model was used to predict VT and auto-PEEP under normal, restrictive, and obstructive conditions. RESULTS: The BPV models tested delivered VT in a similar manner. VT decreased with decreased compliance and increased resistance. Auto-PEEP developed with increased resistance and compliance. The model predicted a VT delivery dependent on inspiratory flow cutoff level. For the obstructive condition, the model predicts an optimal VT delivery within a specific inspiratory flow cutoff range that becomes narrower with increasing resistance. CONCLUSIONS: VT delivery and auto-PEEP generated by BPVs are highly dependent on the prevailing impedance condition. Though there are differences between BPV models, generally, performance was similar between the models tested. This report suggests that knowledge of both respiratory system impedance and the performance of the BPV in use are required to attend to inadequate VT delivery and auto-PEEP generation. Furthermore, the model predicts a relatively narrow range for inspiratory flow cutoff that provides adequate ventilatory support without causing hyperinflation in patients with obstructive conditions.

Humans↗

PubMed1999

Risk neutralization in cardiac operations: detection and treatment of associated carotid disease.

BACKGROUND: A screening and treatment protocol was implemented to extend the benefit of prophylactic carotid endarterectomy to patients who had open heart operations. METHODS: Patients aged 65 or older or who at any age had left main coronary disease, transient ischemic attack, or stroke were eligible for preoperative carotid duplex screening. Carotid endarterectomies and open heart operations were planned as a staged (n = 59) or combined procedure (n = 55) for angiographically confirmed carotid stenosis of at least 80%. RESULTS: Duplex scans were obtained in 1,719 of 7,035 open heart surgical patients over 8 years. The overall stroke rate was 1.5% (108 of 7,035). Seven of these were strokes of carotid origin (0.1%). There were 129 patients with at least 80% stenosis. One hundred fourteen had carotid endarterectomy preceding open heart operation, and none had carotid artery stroke. Twelve patients with at least 80% carotid stenosis by duplex scan had open heart operations without prophylactic carotid endarterectomies. There were four carotid strokes in these 12 patients (p = 0.0001; odds ratio, 20.2). Stroke risk remained significantly elevated (16.8%, p = 0.005) in the 50% to 79% group. The changes associated with the reduced risk afforded by this screening and treatment strategy amounted to $346 for each patient in the study. CONCLUSIONS: The risk of carotid stroke at the time of cardiac operation can be defined by duplex screening. Prophylactic carotid endarterectomy neutralizes the risk in those with at least 80% stenosis. Consideration for lowering the threshold for assessment and treatment of carotid stenoses appears warranted. The economic investment is recouped by the savings in system resources that would have been depleted through care for carotid stroke and its sequelae.

Adult↗

PubMed1999

Interferon beta-1b and childhood multiple sclerosis.

The long-term treatment with interferon beta-1b of a 7-year-old male with relapsing-remitting multiple sclerosis is documented. Thirty-two months after initiating treatment, he demonstrates dramatic clinical improvement, without relapse, despite high titers of neutralizing antibodies to interferon beta-1b. It appears reasonable to attribute a role in his improvement to interferon beta-1b.

Adjuvants, Immunologic↗

PubMed1999

Penetrating cardiac trauma at an urban trauma center: a 22-year perspective.

This is a report of a 22-year experience with penetrating cardiac trauma at a single urban Level I trauma center. We conducted a retrospective chart review supplemented by computerized patient log. Comparisons of mortality between Period 1 (1975-1985; 113 patients) and Period 2 (1986-1996; 79 patients) were by chi2 or Fisher's exact tests. Statistical significance was defined as P < or = 0.05. From 1975 to 1996, 192 patients (mean age, 32 years; 88% male) with penetrating cardiac stab wounds (68%) or gunshot wounds (32%) were treated. The most common initial clinical presentation was cardiac tamponade, and most patients (54%) were hypotensive (systolic blood pressure 30-90 mm Hg). The most common initial intervention in the emergency center was tube thoracostomy. The use of pericardiocentesis as a diagnostic and therapeutic modality in the emergency center virtually disappeared in Period 2, as compared with Period 1. Since 1994, surgeon-performed cardiac ultrasound has been performed and has correctly diagnosed hemopericardium in 12 patients (100% survival). The overall mortality for all patients during the 22-year study interval was 25 per cent and was not significantly different between Period 1 (27%) and Period 2 (22%). The mortality associated with gunshot wounds was increased compared with that of stab wounds. Similarly, mortality for patients who arrested in the emergency center was increased compared with those patients who did not arrest. We conclude: 1) cardiac tamponade is the most common presentation in patients with cardiac wounds; 2) pericardiocentesis in the emergency center has essentially disappeared; 3) surgeon-performed ultrasound of the pericardium should improve survival of future patients who are normotensive or mildly hypotensive; 4) over the last 11 years, there has been a substantial decrease in mortality in patients with stab wounds and a statistically significant decrease in arrested patients; and 5) overall mortality for penetrating cardiac trauma has not changed during the 22-year interval.

Adolescent↗

PubMed1996

Distal effects of tracheal gas insufflation: changes with catheter position and oleic acid lung injury.

We separated distal (turbulence-related) and proximal (dead space washout-related) effects of tracheal gas insufflation (TGI) by comparing the effects of straight and inverted catheters. We reasoned that the inverted catheter was unlikely to remove CO2 from conducting airways distal to its orifice. In six normal dogs during TGI at 10 l/min, advancing the catheters from 10 to 1 cm above the main carina decreased dead space volume by 29 +/- 12 and 12 +/- 6 ml (P < 0.04) with the straight and inverted catheters, respectively. By comparison, the tracheal volume between 10 and 1 cm above the carina was 15 +/- 2 ml. In another set of dogs (n = 5), we examined the distal effects of TGI before and after oleic acid-induced lung injury. During TGI at 10 l/min before and after oleic acid injury, the differences in arterial PCO2 between the straight and inverted catheters were 5 +/- and 9 +/- 6 Torr (P < 0.18), respectively. Our data suggest that distal effects of TGI become more pronounced as the catheter tip is positioned closer to the main carina. The distal effects of TGI were not diminished after oleic acid injury when minute ventilation was maintained constant.

Animals↗

PubMed1996

Tracheal gas insufflation: catheter effectiveness determined by expiratory flush volume.

Used adjunctively during mechanical ventilation, tracheal gas insufflation (TGI) improves CO2 elimination, principally by decreasing effective anatomic dead space. Continuing lung deflation at end- expiration raises the end-expiratory C02 concentration within the proximal airway, and could theoretically reduce the efficiency of a given catheter flow. To test this possibility, we designed a series of experiments that examined the influence of TGI delivery patterns on the efficiency of CO2 elimination. Using a gating device, catheter flow was delivered selectively during desired portions of expiration. Paralyzed, ventilated dogs were studied at short and extended inspiratory time fractions (TI/TT) with inspiratory tidal volume and ventilator frequency held constant. The expiratory flush volume, not the pattern of gas delivery, determined the observed decline in PaCO2, provided that the end-expiratory period was included in the catheter flush period. Despite continuing end-expiratory lung deflation (extended TI/TT), catheter effectiveness remained the same at matched expiratory flush volumes. To determine if enhanced distal mixing at the higher catheter flows required during the extended TI/TT (to match expiratory flush volume) masked a decrease in efficiency, we repeated the experiment with a tip-inverted catheter. We again found that matched catheter delivered expiratory volumes were similarly effective. With or without ongoing lung deflation, the volume of gas flushed during the expiratory period determined the effectiveness of TGI, provided that inspired minute ventilation remains unchanged and end-expiration is included in the catheter flush period.

Analysis of Variance↗

PubMed1995

Inspiratory tidal volume sparing effects of tracheal gas insufflation in dogs with oleic acid-induced lung injury.

PURPOSE: Tracheal gas insufflation (TGI) improves the efficiency of conventional mechanical ventilation (CMV) by reducing the series dead space of the airways. Consequently, application of TGI as an adjunct to CMV may permit reducing tidal volume (VT) while limiting CO2 retention. We tested the extent to which panexpiratory TGI allows reduction of VT while maintaining PaCO2 constant in an oleic acid-induced lung injury model. METHODS: We studied six anesthetized, paralyzed, and mechanically ventilated dogs. Oleic acid injury was induced by injecting 0.09 mL/kg of oleic acid into the right atrium. After stabilization of lung injury the VT-sparing effect of TGI was tested by progressively increasing catheter flow rate (Vc) from 2 to 5, 10, and 15 L/min while decreasing VT by an amount that maintained PaCO2 constant (approximately 47 mm Hg) with respect to baseline (Vc = 0 L/min). RESULTS: Tidal volume was decreased from a baseline value of 0.360 +/- 0.030 L to 0.238 +/- 0.054 L at Vc of 15 L/min. The reduction in VT was associated with a decrement in peak and end-inspiratory plateau airway opening pressure from 32 +/- 3 to 28 +/- 6 cm H2O and from 25 +/- 2 to 21 +/- 3 cm H2O, respectively. Total physiological dead space fraction decreased from a baseline value of 0.60 +/- 0.08 to 0.31 +/- 0.20 during TGI at 15 L/min. TGI did not affect cardiac output, PaO2, or pulmonary venous admixture. CONCLUSION: We conclude that TGI can be a useful adjunct to CMV during acute lung injury to limit VT while avoiding CO2 retention.

Analysis of Variance↗

PubMed1995

Effect of tracheal gas insufflation on gas exchange in canine oleic acid-induced lung injury.

OBJECTIVE: To determine the effect of tracheal gas insufflation on gas exchange in oleic acid-induced lung injury in dogs. DESIGN: Prospective, longitudinal study. SETTING: University research laboratory. SUBJECTS: Five mongrel dogs. INTERVENTIONS: The dogs were anesthetized, paralyzed, and mechanically ventilated. Lung injury was induced by infusing 0.09 mL/kg of oleic acid and pulmonary artery occlusion (wedge) pressure (PAOP) was increased to 15 mm Hg by infusing fluids to enhance pulmonary edema formation. After 60 mins, PAOP was allowed to decrease to 5 mm Hg and was maintained at 5 mm Hg for 60 mins to stabilize the pulmonary edema. We studied the effect of tracheal gas insufflation on gas exchange at low and high end-expiratory lung volumes achieved by a positive end-expiratory pressure of 5 and 12 cm H2O, respectively. The FIO2 values of the ventilator and catheter were equivalent (0.6). Each tracheal gas insufflation stage at low and high end-expiratory lung volume was preceded and followed by conventional mechanical ventilation stages without tracheal gas insufflation. During transitions between conventional mechanical ventilation and tracheal gas insufflation, end-expiratory lung volume was maintained constant by adjusting positive end-expiratory pressure while monitoring esophageal pressure and inductive plethysmography. Tidal volume was maintained constant throughout the protocol (0.40 L). MEASUREMENTS AND MAIN RESULTS. At end stage, we measured PaCO2, PaO2, total physiologic deadspace fraction, and venous admixture, which were 43 +/- 4 torr (5.7 +/- 0.5 kPa), 325 +/- 6 torr (43.3 +/- 0.8 kPa), 53 +/- 3%, and 4.0 +/- 0.3% before oleic acid lung injury, respectively. After oleic acid injury at low end-expiratory lung volume, these variables were 55 +/- 4 torr (7.3 +/- 0.5 kPa), 73 +/- 13 torr (9.7 +/- 1.7 kPa), 61 +/- 4%, and 50 +/- 7%, respectively. During tracheal gas insufflation at low end-expiratory lung volume conditions, PaCO2 and the total physiologic deadspace fraction decreased significantly (p < .05) to 45 +/- 4 torr (6.0 +/- 0.5 kPa) and 50 +/- 5%, respectively. Under high end-expiratory lung volume conditions, PaCO2 and the total physiologic deadspace fraction were 55 +/- 7 torr (7.3 +/- 0.9 kPa) and 61 +/- 6%, respectively; during tracheal gas insufflation, these variables decreased to 43 +/- 4 torr (5.7 +/- 0.5 kPa) and 52 +/- 5%, respectively (p < .05). Increasing end-expiratory lung volume improved both PaO2 and venous admixture (p < .05) but tracheal gas insufflation had no significant effect on oxygenation efficiency when end-expiratory lung volume was held constant. CONCLUSIONS: Tracheal gas insufflation augmented alveolar ventilation effectively in the setting of oleic acid-induced lung injury in dogs. When end-expiratory lung volume and tidal volume were kept constant, tracheal gas insufflation did not affect oxygenation.

Animals↗

PubMed1995

Efficacy of expiratory tracheal gas insufflation in a canine model of lung injury.

Tracheal gas insufflation (TGI) improves the efficiency of CO2 elimination by reducing the CO2-laden dead space of the airways. The effect of TGI on PaCO2 diminishes in the setting of acute lung injury (ALI) because an increased alveolar component dominates the total physiologic dead space. Nevertheless, adopting a strategy of permissive hypercapnia should partially offset the decreased efficacy of TGI by increasing CO2 concentration in the proximal airways. To examine these issues we studied the CO2 removal efficacy of expiratory TGI as an adjunct to conventional mechanical ventilation (CMV) before and after oleic acid-induced lung injury (OAI). We first examined the effect of TGI before and after OAI, keeping tidal volume (VT) and frequency constant, and allowing PaCO2 to increase after OAI. We then tested TGI efficiency after matching PaCO2 after OAI to its pre-OAI level by increasing VT (post-OA/VT stage). PaCO2 was 53 +/- 3, 79 +/- 21, and 52 +/- 4 mm Hg in the pre-OAI, post-OAI, and post-OA/VT stages of CMV, respectively. The corresponding decrements in PaCO2 produced by TGI at a flow rate of 10 L/min were 16 +/- 3, 24 +/- 10, and 10 +/- 2 mm Hg, respectively. TGI decreased total physiologic dead space per breath (VD) by 56, 31, and 28 ml during the pre-OAI, post-OAI, and post-OA/VT stages, respectively. Despite a smaller reduction in VD during the post-OAI stage, the effect of TGI on PaCO2 was preserved because of the relatively high PaCO2 prior to its initiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Air↗

PubMed1995

Spirometry and maximal respiratory pressure references from healthy Minnesota 65- to 85-year-old women and men.

OBJECTIVE: To obtain spirometry and maximal respiratory pressure (MRP) reference values for elderly persons. DESIGN: Survey. SETTING: General community. PARTICIPANTS: Four hundred seventy-one healthy ambulatory white women and men age 65+ years. METHODS: A stringent spirometry quality assurance program exceeded American Thoracic Society recommendations. A "healthy" subgroup of 176 women and 112 men between the ages of 65- and 85 years were identified by excluding those with conditions that negatively influenced FEV1 in a multiple regression analysis. Reference equations and normal ranges for FEV1, FVC, FEF25-75%, peak flow, and maximal inspiratory and expiratory pressures (MRPs) were determined from the healthy group with good quality maneuvers. RESULTS: Less than 10% of the subjects were unable to perform three acceptable spirometry maneuvers and ten MRP maneuvers. When the age and height corrected FEV1s from this group were compared with other spirometry reference studies, mean values from the women were nearly identical to those from Morris, while these men had substantially lower FEV1 values (by 0.3- to 0.5L) than elderly men in Crapo's study. Mean peak flow was over 20% higher when compared with previous studies, suggesting greater initial expiratory effort by our subjects. The maximal inspiratory pressure (MIP) values were about 20% higher than those reported by the Cardiovascular Health Study, perhaps because five MIP maneuvers were always performed. CONCLUSION: Spirometry and MRP reference values used for elderly patients should come from population studies using similar techniques and with large numbers of subjects over age 65 years.

Age Distribution↗

PubMed1994

Irreversible hydrocolloids: a comparison of antimicrobial efficacy.

The surface antimicrobial efficacy of four irreversible hydrocolloid materials against two common oral bacteria, Lactobacillus and Streptococcus mutans, was evaluated. Twelve reversible hydrocolloid (agar) plates for each bacteria were used. Five wells, 1 cm in diameter by 5 ml in depth, were punched into each plate that contained a known concentration of bacteria. An equal-sized but different type of irreversible hydrocolloid plug was placed into each of four wells. The fifth (center) well contained chlorhexidine (Peridex) as a positive control agent. Results indicated that the irreversible hydrocolloids Coe Hydrophilic Gel (CHG) with chlorhexidine and Jeltrate Plus with quaternary ammonium were both as effective as the positive control agent in reducing surface growth of the bacteria studied. The use of antimicrobial irreversible hydrocolloids thus may aid in reducing operatory to laboratory cross-contamination.

Chlorhexidine↗

PubMed1994

Implications of a biphasic two-compartment model of constant flow ventilation for the clinical setting.

PURPOSE: To investigate the theoretical effects of changing frequency (f), duty cycle (D), or end-inspiratory pause length on the distribution of ventilation and compartmental pressure in a heterogeneous, two compartment pulmonary model inflated by constant flow. METHODS: Differential equations governing compartmental volume changes were derived and solved. Validation was conducted in a mechanical lung analogue with two mechanically independent compartments. Model predictions were then generated over wide ranges of f, D, or end-inspiratory pause. RESULTS: Disparity of compartmental end-expiratory pressure was identified as the primary mechanism by which changes in f, D, or pause alter the distribution of ventilation. Distribution of peak pressures was less sensitive to such changes. Compartmental ventilation was much less uniform than compartmental peak pressure. Ventilation could not be made entirely uniform by changes of f, D, or pause within the usual clinical range. CONCLUSIONS: In a linear, two compartment model of the respiratory system, disparity of compartmental end-expiratory pressures is the primary mechanism by which changes of f, D, or pause alter the distribution of ventilation during inflation with constant flow. Ventilation is less evenly distributed than peak alveolar pressure, and there are limits to the beneficial effects on the distribution of ventilation to be gained from manipulations of machine settings.

Evaluation Studies as Topic↗

PubMed1994

Effect of a nasogastric tube on esophageal pressure measurement in normal adults.

We studied the correspondence between fluctuations of esophageal pressure measured before and after placement of a nasogastric (NG) tube in six normal volunteers. Flow, airway pressure, and esophageal pressure data from at least 20 breaths were recorded in seven ventilatory conditions in two body postures: 0 degree (supine) and 60 degrees (upright). The conditions studied included normal quiet breathing, added resistance, reduced compliance, increased frequency, increased tidal volume, continuous positive airway pressure, and volume-cycled ventilation with positive pressure. During recording with the NG tube in place, the subject targeted the same tidal volume (VT), respiratory rate, and inspiratory time fraction (TI/TTOT) recorded before NG tube placement. A computer program selected for analysis only those recorded breaths with and without an NG tube that were "matched" within 5 percent for both VT and TI. We calculated average VT, TI, and esophageal pressure fluctuation (delta Pes) for the matched breaths from each subject during every condition. The delta Pes values with and without NG tube were not statistically different in any tested condition (p > 0.05). Our data indicate that the presence of an NG tube does not invalidate the accuracy of delta Pes measurements made using a well-positioned balloon catheter in the tested conditions.

Adult↗

PubMed1993

Comparison of mathematical and mechanical models of pressure-controlled ventilation.

Recent evidence that volume-cycled mechanical ventilation may itself produce lung injury has focused clinical attention on the pressure waveform applied to the respiratory system. There has been an increasing use of pressure-controlled ventilation (PCV), because it limits peak cycling pressure and provides a decelerating flow profile that may improve gas exchange. In this mode, however, the relationships are of machine adjustments to ventilation and alveolar pressure are not straightforward. Consequently, setting selection remains largely an empirical process. In previous work, we developed a biexponential model of PCV that provides a conceptual framework for understanding these interactions (J. Appl. Physiol. 67: 1081-1092, 1989). We tested the validity of this mathematical model in a single-compartment analogue of the respiratory system across wide ranges of clinician-set variables (frequency, duty cycle, applied pressure) and impedance conditions (inspiratory and expiratory resistance and system compliance). Our data confirm the quantitative validity of the proposed model when approximately rectilinear waves of pressure are applied and appropriate values for impedance are utilized. Despite a fixed-circuit configuration, however, resistance proved to be a function of each clinician-set variable, requiring remeasurement of system impedance as adjustments in these variables were made. With further modification, this model may provide a practical as well as a conceptual basis for understanding minute ventilation and alveolar pressure fluctuations during PCV in the clinical setting.

Air Pressure↗

PubMed1993

Effect of catheter flow direction on CO2 removal during tracheal gas insufflation in dogs.

Tracheal gas insufflation (TGI) improves the efficiency of CO2 elimination by replacing CO2 in the anatomic dead space proximal to the catheter tip with fresh gas during expiration. Turbulence generated by gas exiting the catheter tip may also contribute to alveolar ventilation. To separate distal (turbulence-related) and proximal (washout of dead space) effects of TGI, we compared the efficacy of a straight and an inverted catheter during continuous and expiratory TGI in six mechanically ventilated dogs. We reasoned that the inverted catheter cannot improve CO2 elimination from more distal conducting airways. During continuous TGI with the straight catheter, arterial PCO2 (PaCO2) decreased significantly from baseline (without TGI) of 56 +/- 10 Torr to 38 +/- 8, 36 +/- 8, and 35 +/- 8 Torr at catheter flow rates (Vcath) of 5, 10, and 15 l/min, respectively. For the same conditions, PaCO2 was always higher (P < 0.001) with the inverted catheter (42 +/- 10, 41 +/- 10, and 41 +/- 10 Torr). PaCO2 was lower with the straight (40 +/- 9 Torr) than with the inverted catheter (44 +/- 10 Torr, P < 0.001) during TGI delivered only during expiration at a Vcath of 10 l/min. End-expiratory lung volume relative to baseline increased during continuous, but not during expiratory, TGI and was significantly greater with the straight than with the inverted catheter (P < 0.0001). Our data confirm that the primary mechanism of TGI is expiratory washout of the proximal anatomic dead space but also suggest a minor contribution of turbulence beyond the tip of the straight catheter.

Animals↗

PubMed1993

Tracheal gas insufflation augments CO2 clearance during mechanical ventilation.

A technique that improves the efficiency of alveolar ventilation should decrease the pressure required and reduce the potential for lung injury during mechanical ventilation. Alveolar ventilation may be improved by replacing a portion of the anatomic dead space with fresh gas via an intratracheal catheter. We studied the effect of intratracheal gas insufflation as an adjunct to volume cycled ventilation in eight sedated, paralyzed patients with a variety of lung disorders. Continuous flows of 2, 4, and 6 L/min were delivered through a catheter positioned 1 or 10 cm above the carina. Carbon dioxide production, inspiratory minute ventilation, and peak and mean airway pressures did not change over the range of flows tested. PaCO2 and dead space volume/tidal volume decreased significantly as joint functions of catheter flow and position (p < 0.001). The highest catheter flow (6 L/min) and most distal catheter position (1 cm above the carina) were the most effective combination tested, averaging a 15% reduction in PaCO2 (range 9 to 23%). Certain characteristics of the expiratory capnogram were helpful in predicting the observed reduction in PaCO2. Tracheal gas insufflation may eventually prove a useful adjunct to a pressure-targeted strategy of ventilatory management (in either volume-cycled or pressure controlled modes), particularly when the total dead space is heavily influenced by its anatomic component.

Adult↗

PubMed1993

Modes of tracheal gas insufflation. Comparison of continuous and phase-specific gas injection in normal dogs.

Tracheal gas insufflation (TGI) improves the efficiency of CO2 elimination accomplished by conventional mechanical ventilation, primarily by reducing the anatomic (series) dead space volume. Dead space proximal to the catheter tip can be reduced by two methods. Fresh gas introduced at the carinal level during inspiration may effectively "bypass" the upper airway. Alternatively, proximal dead space can be "washed out" with fresh gas during expiration to reduce CO2 rebreathing. We examined these two modes of TGI-aided dead space reduction in nine paralyzed normal dogs receiving conventional mechanical ventilation and compared these results to those obtained with a catheter that delivered fresh gas continuously at the same flow rate, thereby accomplishing both bypass and washout. Total inspired tidal volume and cycling frequency were held constant. Differences in CO2 elimination efficiency among the TGI modes were flow dependent. Continuous catheter flow at 5 or 10 L/min reduced PaCO2 and physiologic dead space fraction (VD/VT) more than either proximal bypass or end-expiratory washout (p < 0.001). At the same catheter flow settings expiratory washout tended to improve VD/VT more than did inspiratory bypass. Under the conditions tested, constant tracheal insufflation of fresh gas improves alveolar ventilation by mechanisms that include, but are not limited to, a functional reduction in the dead space proximal to the catheter tip.

Analysis of Variance↗

PubMed1993

Surveys of long-term ventilatory support in Minnesota: 1986 and 1992.

To determine the prevalence and some characteristics of persons in Minnesota receiving long-term ventilatory support (ventilator-assisted individuals [VAIs]), we conducted a survey of this population in Minnesota in 1986 and then again in 1992 by canvassing long-term care units and home medical equipment providers. The number of VAIs in 1992 was 110 percent greater than in 1986 (216 vs 103). In 1986, 81 percent of these patients received care at home; the remaining patients were supported in long-term care facilities. By 1992, the percentage had changed to 65 percent supported in the home and 35 percent in long-term care facilities. In both surveys, the largest number of VAIs were in the diagnostic categories of poliomyelitis, cervical trauma, amyotrophic lateral sclerosis (ALS), chronic obstructive pulmonary disease (COPD), and muscular dystrophy. The primary diagnoses with the greatest increase in number of patients were cervical trauma and ALS. When VAIs were categorized by age groups, there was a large increase in the proportion of patients younger than 10 years of age and older than 60 years of age. While the number of patients is small, the total resources required for care of these patients can be substantial. These data suggest that we need to monitor the number and demographic characteristics of VAIs in the United States so that appropriate policies and programs are developed to provide effective support services.

Adolescent↗