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1.
Adv Physiol Educ ; 46(2): 282-285, 2022 Jun 01.
Artículo en Inglés | MEDLINE | ID: mdl-35201919

RESUMEN

While the effects of changing heart rate and systemic vascular resistance have been generally understood and appreciated, the effects of changes in left ventricular contractility on end-systolic volume may have been less understood and appreciated and the effects of changes in venous capacitance on end-diastolic volume may have been unknown to many readers. Herein, we have provided a brief review for the medical student and beginning graduate student highlighting these sometimes-complex relationships.


Asunto(s)
Ventrículos Cardíacos , Presorreceptores , Presión Sanguínea , Frecuencia Cardíaca , Humanos , Presorreceptores/fisiología , Resistencia Vascular/fisiología
2.
Optom Vis Sci ; 99(4): 389-393, 2022 04 01.
Artículo en Inglés | MEDLINE | ID: mdl-35001064

RESUMEN

SIGNIFICANCE: Severe acute respiratory syndrome coronavirus 2 has indirectly created challenges to the ophthalmic retinal examinations because of lens fogging related to patients wearing masks. To date, there are no objective data on the degree of diagnostic ophthalmic lens fogging associated with mask wearing or on the effectiveness of proposed solutions to ophthalmologic lens fogging. PURPOSE: The purposes of this study were to investigate the degree of ophthalmologic lens fogging in patients wearing masks and to assess the efficacy lens warming in reducing lens fogging and facilitating ophthalmologic retinal examinations. METHODS: This study quantified the degree of lens fogging in mask-wearing subjects using ImageJ to measure lens surface area fogged in slit-lamp photographs of 90 D lenses before and after the use of a lens warmer. We investigated the clinical relevance of diagnostic lens fogging via a survey study of eye care providers. Subjects rated on a Likert scale their experience with diagnostic lens fogging during retinal examination in mask-wearing patients with and without the use of a lens warming device. RESULTS: For mask-wearing subjects, the percentage of fogged lens area in a 90 D lens averaged 32.5% using an unheated lens and 1.1% using a heated lens. Survey responders noted significantly less fogging of the 78 and 90 D lenses on retinal examination when using the lens warmer (P < .001) and found that using the lens warmer facilitated their retinal examination (P < .001). CONCLUSIONS: This study shows that there is significant fogging of ophthalmic slit-lamp lenses associated with patients wearing masks and that using a lens warmer significantly reduces fogging and facilitates retinal examinations. Eye care providers would benefit from the use of a lens warmer to reduce diagnostic lens fogging during retinal examination.


Asunto(s)
COVID-19 , Cristalino , Lentes , COVID-19/epidemiología , COVID-19/prevención & control , Humanos , Microscopía con Lámpara de Hendidura , Pruebas de Visión
3.
Adv Physiol Educ ; 41(3): 348-353, 2017 Sep 01.
Artículo en Inglés | MEDLINE | ID: mdl-28679570

RESUMEN

Because the heart and lungs are confined within the thoracic cavity, understanding their interactions is integral for studying each system. Such interactions include changes in external constraint to the heart, blood volume redistribution (venous return), direct ventricular interaction (DVI), and left ventricular (LV) afterload. During mechanical ventilation, these interactions can be amplified and result in reduced cardiac output. For example, increased intrathoracic pressure associated with mechanical ventilation can increase external constraint and limit ventricular diastolic filling and, therefore, output. Similarly, high intrathoracic pressures can alter blood volume distribution and limit diastolic filling of both ventricles while concomitantly increasing pulmonary vascular resistance, leading to increased DVI, which may further limit LV filling. While LV afterload is generally considered to decrease with increased intrathoracic pressure, the question arises if the reduced LV afterload is primarily a consequence of a reduced LV preload. A thorough understanding of the interaction between the heart and lungs can be complicated but is essential for clinicians and health science students alike. In this teaching review, we have attempted to highlight the present understanding of certain salient aspects of cardiopulmonary physiology and pathophysiology, as well as provide a resource for multidisciplined health science educators and students.


Asunto(s)
Corazón/fisiología , Pulmón/fisiología , Fisiología/educación , Humanos
4.
Vascul Pharmacol ; 79: 24-31, 2016 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-26239885

RESUMEN

SKA-31, an activator of endothelial KCa2.3 and KCa3.1 channels, reduces systemic blood pressure in mice and dogs, however, its effects in larger mammals are not well known. We therefore examined the hemodynamic effects of SKA-31, along with sodium nitroprusside (SNP), in anesthetized, juvenile male domestic pigs. Experimentally, continuous measurements of left ventricular (LV), aortic and inferior vena cava (IVC) pressures, along with flows in the ascending aorta, carotid artery, left anterior descending coronary artery and renal artery, were performed during acute administration of SKA-31 (0.1, 0.3, 1.0, 3.0 and 5.0mg/ml/kg) and a single dose of SNP (5.0 µg/ml/kg). SKA-31 dose-dependently reduced mean aortic pressure (mPAO), with the highest dose decreasing mPAO to a similar extent as SNP (-23 ± 3 and -28 ± 4 mmHg, respectively). IVC pressure did not change. Systemic conductance and conductance in coronary and carotid arteries increased in response to SKA-31 and SNP, but renal artery conductance was unaffected. There was no change in either LV stroke volume (SV) or heart rate (versus the preceding control) for any infusion. With no change in SV, drug-evoked decreases in LV stroke work (SW) were attributed to reductions in mPAO (SW vs. mPAO, r(2)=0.82, P<0.001). In summary, SKA-31 dose-dependently reduced mPAO by increasing systemic and arterial conductances. Primary reductions in mPAO by SKA-31 largely account for associated decreases in SW, implying that SKA-31 does not directly impair cardiac contractility.


Asunto(s)
Presión Arterial/efectos de los fármacos , Benzotiazoles/farmacología , Endotelio Vascular/efectos de los fármacos , Canales de Potasio de Conductancia Intermedia Activados por el Calcio/agonistas , Canales de Potasio de Pequeña Conductancia Activados por el Calcio/agonistas , Animales , Presión Arterial/fisiología , Relación Dosis-Respuesta a Droga , Endotelio Vascular/metabolismo , Canales de Potasio de Conductancia Intermedia Activados por el Calcio/metabolismo , Masculino , Canales de Potasio de Pequeña Conductancia Activados por el Calcio/metabolismo , Sus scrofa , Porcinos
6.
J Neuroophthalmol ; 35(4): 353-9, 2015 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-26035806

RESUMEN

BACKGROUND: The goal of our study was to look for the presence of homonymous ganglion cell layer-inner plexiform layer complex (GCL-IPL) thinning using spectral-domain optical coherence tomography (SD-OCT) in patients with a history of adult-onset injury to the postgeniculate pathways with rigorous radiological exclusion of geniculate and pregeniculate pathology. METHODS: We performed a retrospective review of twenty-two patients (ages 24-75 y, 6 men, 16 women) with homonymous visual field (VF) defects secondary to postgeniculate injury examining the GCL-IPL with SD-OCT. An additional fifteen patients (ages 28-85 y, 5 men, 10 women) with no visual pathway pathology served as controls. Using segmentation analysis software applied to the macular scan, a normalized asymmetry score was calculated for each eye comparing GCL-IPL thickness ipsilateral vs contralateral to the patient's brain lesions. RESULTS: We found that 15 of the twenty-two subjects had a relative thinning of the GCL-IPL ipsilateral to the postgeniculate lesion in both eyes (represented by a positive normalized asymmetry score in both eyes), whereas a similar pattern of right/left asymmetry was found in 4 controls (P = 0.0498). The magnitude of asymmetry was much greater in subjects compared with controls (P = 0.0004). There was no association between the degree of GCL-IPL thinning and the mean deviation on automated VF testing. A moderate correlation (R = 0.782, P = 0.004) between the magnitude of thinning and latency from onset of retrogeniculate injury was observed only after excluding patients beyond a cutoff point of 150 months. CONCLUSIONS: This data provides compelling new evidence of retrograde transsynaptic degeneration causing retinal ganglion cell loss after postgeniculate visual pathway injury.


Asunto(s)
Hemianopsia/patología , Fibras Nerviosas/patología , Células Ganglionares de la Retina/patología , Adulto , Anciano , Anciano de 80 o más Años , Atrofia/etiología , Atrofia/patología , Femenino , Hemianopsia/complicaciones , Humanos , Estudios Longitudinales , Imagen por Resonancia Magnética , Masculino , Persona de Mediana Edad , Estudios Retrospectivos , Tomografía de Coherencia Óptica , Pruebas del Campo Visual , Vías Visuales/patología , Adulto Joven
7.
Adv Physiol Educ ; 38(2): 170-5, 2014 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-24913453

RESUMEN

Dr. Carl Wiggers' careful observations have provided a meaningful resource for students to learn how the heart works. Throughout the many years from his initial reports, the Wiggers diagram has been used, in various degrees of complexity, as a fundamental tool for cardiovascular instruction. Often, the various electrical and mechanical plots are the novice learner's first exposure to simulated data. As the various temporal relationships throughout a heartbeat could simply be memorized, the challenge for the cardiovascular instructor is to engage the learner so the underlying mechanisms governing the changing electrical and mechanical events are truly understood. Based on experience, we suggest some additions to the Wiggers diagram that are not commonly used to enhance cardiovascular pedagogy. For example, these additions could be, but are not limited to, introducing the concept of energy waves and their role in influencing pressure and flow in health and disease. Also, integrating concepts of exercise physiology, and the differences in cardiac function and hemodynamics between an elite athlete and normal subject, can have a profound impact on student engagement. In describing the relationship between electrical and mechanical events, the instructor may find the introduction of premature ventricular contractions as a useful tool to further understanding of this important principle. It is our hope that these examples can aid cardiovascular instructors to engage their learners and promote fundamental understanding at the expense of simple memorization.


Asunto(s)
Corazón/fisiología , Aprendizaje , Ilustración Médica , Fisiología/educación , Enseñanza/métodos , Comprensión , Curriculum , Sistema de Conducción Cardíaco/fisiopatología , Hemodinámica , Humanos , Memoria , Factores de Tiempo , Función Ventricular
9.
Physiol Rep ; 2(3): e00259, 2014.
Artículo en Inglés | MEDLINE | ID: mdl-24760513

RESUMEN

Abstract High-frequency oscillatory ventilation (HFOV) may improve gas exchange in patients who are inadequately ventilated by conventional mechanical ventilation (CV); however, the hemodynamic consequences of switching to HFOV remain unclear. We compared the effects of CV and HFOV on pulmonary vascular conductance and left ventricular (LV) preload and performance at different airway and filling pressures. In anesthetized dogs, we measured LV dimensions, aortic and pulmonary artery (PA) flow, and mean airway ( AW) and pericardial pressures. Catheter-tip pressure manometers measured aortic, LV, left atrial, and PA pressures. The pericardium and chest were closed. At LV end-diastolic pressure (PLVED) = 5 mmHg and 12 mmHg, PEEP was varied (6 cm H2O, 12 cm H2O, and 18 cm H2O) during CV. Then, at airway pressures equal to those during CV, HFOV was applied at 4 Hz, 10 Hz, and 15 Hz. Increased AW decreased pulmonary vascular conductance. As cardiac output increased, conductance increased. At PLVED = 12 mmHg, conductance was greatest during HFOV at 4 Hz. LV preload (i.e., ALV, our index of end-diastolic volume) was similar during HFOV and CV for all conditions. At PLVED = 12 mmHg, SWLV was similar during CV and HFOV, but, at PLVED = 5 mmHg and AW 10 cm H2O, SWLV was lower during HFOV than CV. Compared to pulmonary vascular conductance at higher frequencies, at PLVED = 12 mmHg, conductance was greater at HFOV of 4 Hz. Effects of CV and HFOV on LV preload and performance were similar except for decreased SWLV at PLVED = 5 mmHg. These observations suggest the need for further studies to assess their potential clinical relevance.

10.
J Appl Physiol (1985) ; 112(3): 396-402, 2012 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-22096121

RESUMEN

Vascular neck restraint (VNR) is a technique that police officers may employ to control combative individuals. As the mechanism of unconsciousness is not completely understood, we tested the hypothesis that VNR simply compresses the carotid arteries, thereby decreasing middle cerebral artery blood flow. Twenty-four healthy police officers (age 35 ± 4 yr) were studied. Heart rate (HR), arterial pressure, rate of change of pressure (dP/dt), and stroke volume (SV) were measured using infrared finger photoplethysmography. Bilateral mean middle cerebral artery flow velocity (MCAVmean) was measured by using transcranial Doppler ultrasound. Neck pressure was measured using flat, fluid-filled balloon transducers positioned over both carotid bifurcations. To detect ocular fixation, subjects were asked to focus on a pen that was moved from side to side. VNR was released 1-2 s after ocular fixation. Ocular fixation occurred in 16 subjects [time 9.5 ± 0.4 (SE) s]. Pressures over the right (R) and left (L) carotid arteries were 257 ± 22 and 146 ± 18 mmHg, respectively. VNR decreased MCAVmean (R 45 ± 3 to 8 ± 4 cm/s; L 53 ± 2 to 10 ± 3 cm/s) and SV (92 ± 4 to 75 ± 4 ml; P < 0.001). Mean arterial pressure (MAP), dP/dt, and HR did not change significantly. We conclude that the most important mechanism in loss of consciousness was decreased cerebral blood flow caused by carotid artery compression. The small decrease in CO (9.6 to 7.5 l/min) observed would not seem to be important as there was no change in MAP. In addition, with no significant change in HR, ventricular contractility, or MAP, the carotid sinus baroreceptor reflex appears to contribute little to the response to VNR.


Asunto(s)
Arterias Carótidas/fisiología , Circulación Cerebrovascular/fisiología , Estado de Conciencia/fisiología , Arteria Cerebral Media/fisiología , Restricción Física/métodos , Adulto , Velocidad del Flujo Sanguíneo/fisiología , Presión Sanguínea/fisiología , Seno Carotídeo/fisiología , Ojo , Femenino , Fijación Ocular/fisiología , Frecuencia Cardíaca/fisiología , Hemodinámica/fisiología , Humanos , Masculino , Cuello/fisiología , Presorreceptores/fisiología , Restricción Física/efectos adversos , Volumen Sistólico/fisiología , Adulto Joven
11.
Am J Physiol Regul Integr Comp Physiol ; 300(3): R763-70, 2011 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-21228338

RESUMEN

During mechanical ventilation, increased pulmonary vascular resistance (PVR) may decrease right ventricular (RV) performance. We hypothesized that volume loading, by reducing PVR, and, therefore, RV afterload, can limit this effect. Deep anesthesia was induced in 16 mongrel dogs (8 oleic acid-induced acute lung injury and 8 controls). We measured ventricular pressures, dimensions, and stroke volumes during positive end-expiratory pressures of 0, 6, 12, and 18 cmH(2)O at three left ventricular (LV) end-diastolic pressures (5, 12, and 18 mmHg). Oleic acid infusion (0.07 ml/kg) increased PVR and reduced respiratory system compliance (P < 0.05). With positive end-expiratory pressure, PVR was greater at a lower LV end-diastolic pressure. Increased PVR was associated with a decreased transseptal pressure gradient, suggesting that leftward septal shift contributed to decreased LV preload, in addition to that caused by external constraint. Volume loading reduced PVR; this was associated with improved RV output and an increased transseptal pressure gradient, which suggests that rightward septal shift contributed to the increased LV preload. If PVR is used to reflect RV afterload, volume loading appeared to reduce PVR, thereby improving RV and LV performance. The improvement in cardiac output was also associated with reduced external constraint to LV filling; since calculated PVR is inversely related to cardiac output, increased LV output would reduce PVR. In conclusion, our results, which suggest that PVR is an independent determinant of cardiac performance, but is also dependent on cardiac output, improve our understanding of the hemodynamic effects of volume loading in acute lung injury.


Asunto(s)
Lesión Pulmonar Aguda/terapia , Respiración con Presión Positiva , Circulación Pulmonar , Resistencia Vascular , Disfunción Ventricular Derecha/prevención & control , Función Ventricular Derecha , Lesión Pulmonar Aguda/inducido químicamente , Lesión Pulmonar Aguda/fisiopatología , Animales , Modelos Animales de Enfermedad , Perros , Femenino , Rendimiento Pulmonar , Masculino , Modelos Cardiovasculares , Ácido Oléico , Respiración con Presión Positiva/efectos adversos , Volumen Sistólico , Disfunción Ventricular Derecha/etiología , Disfunción Ventricular Derecha/fisiopatología , Función Ventricular Izquierda , Presión Ventricular
12.
Alcohol Clin Exp Res ; 29(9): 1672-6, 2005 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-16205367

RESUMEN

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.


Asunto(s)
Consumo de Bebidas Alcohólicas/sangre , Etanol/sangre , Adulto , Consumo de Bebidas Alcohólicas/psicología , Femenino , Humanos , Masculino , Análisis de Regresión , Factores Sexuales , Estudiantes , Universidades
13.
Alcohol Clin Exp Res ; 29(4): 631-8, 2005 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-15834229

RESUMEN

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.


Asunto(s)
Consumo de Bebidas Alcohólicas/psicología , Estudiantes/psicología , Adolescente , Adulto , Recolección de Datos , Retroalimentación Psicológica , Femenino , Humanos , Masculino , Asunción de Riesgos , Universidades
14.
Am J Physiol Heart Circ Physiol ; 289(2): H549-57, 2005 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-15792988

RESUMEN

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.


Asunto(s)
Circulación Coronaria/fisiología , Respiración Artificial , Función Ventricular Izquierda , Función Ventricular Derecha , Abdomen , Animales , Apnea/fisiopatología , Perros , Femenino , Hemodinámica , Inhalación , Masculino , Presión , Vasoconstricción , Vena Cava Inferior/fisiología
15.
Can J Cardiol ; 21(1): 73-81, 2005 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-15685307

RESUMEN

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.


Asunto(s)
Hemodinámica/fisiología , Respiración con Presión Positiva/métodos , Circulación Pulmonar/fisiología , Resistencia Vascular/fisiología , Función Ventricular Izquierda/fisiología , Anestesia , Animales , Perros , Femenino , Pruebas de Función Cardíaca , Masculino , Modelos Animales , Análisis Multivariante , Probabilidad , Análisis de Regresión , Respiración Artificial , Medición de Riesgo
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