Biomedical subjects

Jamie R Mitchell

Publications and source records attributed to Jamie R Mitchell.

4 recordsLinked to original sources

PubMed2005

RV filling modulates LV function by direct ventricular interaction during mechanical ventilation.

During mechanical ventilation, phasic changes in systemic venous return modulate right ventricular output but may also affect left ventricular function by direct ventricular interaction. In 13 anesthetized, closed-chest, normal dogs, we measured inferior vena cava flow and left and right ventricular dimensions and output during mechanical ventilation, during an inspiratory hold, and (during apnea) vena caval constriction and abdominal compression. During a single ventilation cycle preceded by apnea, positive pressure inspiration decreased caval flow and right ventricular dimension; the transseptal pressure gradient increased, the septum shifted rightward, reflecting an increased left ventricular volume (the anteroposterior diameter did not change); and stroke volume increased. The opposite occurred during expiration. Similarly, the maneuvers that decreased venous return shifted the septum rightward, and left ventricular volume and stroke volume increased. Increased venous return had opposite effects. Changes in left ventricular function caused by changes in venous return alone were similar to those during mechanical ventilation except for minor quantitative differences. We conclude that phasic changes in systemic venous return during mechanical ventilation modulate left ventricular function by direct ventricular interaction.

Abdomen↗

PubMed2005

College students lack knowledge of standard drink volumes: implications for definitions of risky drinking based on survey data.

BACKGROUND: College students tend to pour single servings of beer and liquor that are larger than commonly used standards. The reasons for this are unknown. Students might overpour because they lack knowledge of standard serving sizes. Alternatively, they might know how much alcohol to pour but simply have difficulty pouring the correct amounts. Misperceptions of standard serving sizes could lead to inaccuracies in self-reported consumption. If this is the case, then the validity of students' responses on alcohol surveys and the definitions of risky drinking that are based on them would be called into question. This study examined how college students define standard drinks, whether their definitions are similar to the definitions commonly used by alcohol researchers and government agencies, and whether their definitions of standard drinks are related to the sizes of the drinks that they pour. The study also examined whether feedback regarding the accuracy of their definitions of standard drinks leads students to alter their self-reported levels of consumption. METHODS: Students (N = 133) completed an alcohol survey and performed tasks that required them to free-pour a single beer, glass of wine, shot of liquor, or the amount of liquor in a mixed drink. Roughly half of the students received feedback regarding their definitions of standard drinks. All students then were resurveyed about their recent levels of consumption. RESULTS: With the exception of beer, students incorrectly defined the volumes of standard servings of alcohol, overestimating the appropriate volumes. They also overestimated appropriate volumes when asked to free-pour drinks. Positive relationships existed between students' definitions of standard drinks and the sizes of the drinks that they free-poured. Feedback regarding misperceptions of standard drink volumes led to an increase in levels of self-reported consumption, suggesting that students' original estimates of their alcohol consumption were too low. CONCLUSIONS: Despite the recent focus on alcohol education and prevention at the college level, college students have not been taught how to define standard drinks accurately. They tend to overstate the appropriate volumes, leading them to overpour drinks and underreport levels of consumption. Self-reported consumption levels are altered by feedback regarding the accuracy of students' definitions of standard drinks. The findings raise important questions about the validity of students' responses on alcohol surveys and the definitions of risky drinking that are based them.

Adolescent↗

PubMed2005

Inconsistencies between actual and estimated blood alcohol concentrations in a field study of college students: do students really know how much they drink?

BACKGROUND: Alcohol use by college students is commonly measured through the use of surveys. The validity of such data hinge on the assumption that students are aware of how much alcohol they actually consume. Recent studies call this assumption into question. Students tend to overestimate the appropriate sizes of standard drinks, suggesting that they might underestimate how much alcohol they consume. If this is true, then students' actual blood alcohol concentrations (BACs) should be higher than BACs estimated based on self-report data. The present study examined this issue METHODS: Breathalyzer readings and self-reported drinking data were collected from 152 college students during the fall of 2004. Estimated BACs were calculated by means of a standard formula, and the relation between actual and estimated BACs was examined. Factors contributing to discrepancies between the two values were identified RESULTS: Estimated BAC levels were significantly higher, not lower, than breath BAC measures. The accuracy of estimated BACs decreased as the number of drinks and amount of time spent drinking increased. Being male and drinking only beer predicted greater accuracy of estimated BACs CONCLUSIONS: Although laboratory data suggest that students underestimate how much they drink, the hypothesis was not supported by data collected in the field. It appears that students might actually overestimate rather than underestimate their levels of consumption when surveyed in the midst of a night of drinking. The findings corroborate observations made by other researchers and suggest that the findings of laboratory studies on college drinking do not necessarily extend to real-world settings.

Adult↗

PubMed2005

Ventricular interaction during mechanical ventilation in closed-chest anesthetized dogs.

The cardiac effects of positive pressure ventilation and positive end-expiratory pressure are incompletely understood. External constraint due to increased intrathoracic pressure decreases left ventricular end-diastolic volume; the effects on venous return and ventricular interaction are less clear. Phasic changes in inferior vena caval flow, end-diastolic ventricular dimensions and output were measured in seven anesthetized, ventilated normal dogs. During inspiration, caval flow, right ventricular diameter and output decreased; end-diastolic transseptal pressure gradient, septum-to-left ventricular free wall diameter, left ventricular area (ie, left ventricular volume index) and output increased despite the decreased sum of the septum-to-free wall diameters. The reverse occurred during expiration. Increased positive end-expiratory pressure decreased the left ventricular area, but the end-expiratory right ventricular diameter was unchanged. At given airway pressures, right ventricular diameter was greater at higher positive end-expiratory pressures, suggesting that a leftward septal shift (direct ventricular interaction) added to the effect of external constraint on left ventricular end-diastolic volume. In conclusion, positive pressure ventilation reduced right ventricular end-diastolic volume during inspiration and increased the transseptal pressure gradient, which shifted the septum rightward, increasing left ventricular end-diastolic volume and output. The reverse occurred during expiration. Positive end-expiratory pressure constrained left ventricular filling and decreased left ventricular end-diastolic volume further by a leftward septal shift.

Anesthesia↗