Large language models generate functional protein sequences across diverse families

Deep-learning language models have shown promise in various biotechnological applications, including protein design and engineering. Here we describe ProGen, a language model that can generate protein sequences with a predictable function across large protein families, akin to generating grammatically and semantically correct natural language sentences on diverse topics. The model was trained on 280 million protein sequences from >19,000 families and is augmented with control tags specifying protein properties. ProGen can be further fine-tuned to curated sequences and tags to improve controllable generation performance of proteins from families with sufficient homologous samples. Artificial proteins fine-tuned to five distinct lysozyme families showed similar catalytic efficiencies as natural lysozymes, with sequence identity to natural proteins as low as 31.4%. ProGen is readily adapted to diverse protein families, as we demonstrate with chorismate mutase and malate dehydrogenase.

Specific lid-base contacts in the 26s proteasome control the conformational switching required for substrate degradation

The 26S proteasome is essential for proteostasis and the regulation of vital processes through ATP-dependent degradation of ubiquitinated substrates. To accomplish the multi-step degradation process, the proteasome's regulatory particle, consisting of lid and base subcomplexes, undergoes major conformational changes whose origin is unknown. Investigating the Saccharomyces cerevisiae proteasome, we found that peripheral interactions between the lid subunit Rpn5 and the base AAA+ ATPase ring are important for stabilizing the substrate-engagement-competent state and coordinating the conformational switch to processing states upon substrate engagement. Disrupting these interactions perturbs the conformational equilibrium and interferes with degradation initiation, while later processing steps remain unaffected. Similar defects in early degradation steps are observed when eliminating hydrolysis in the ATPase subunit Rpt6, whose nucleotide state seems to control proteasome conformational transitions. These results provide important insight into interaction networks that coordinate conformational changes with various stages of degradation, and how modulators of conformational equilibria may influence substrate turnover.

Understanding the 26S proteasome molecular machine from a structural and conformational dynamics perspective

The 26S proteasome is the essential compartmental protease in eukaryotic cells required for the ubiquitin-dependent clearance of damaged polypeptides and obsolete regulatory proteins. Recently, a combination of high-resolution structural, biochemical, and biophysical studies has provided crucial new insights into the mechanisms of this fascinating molecular machine. A multitude of new cryo-electron microscopy structures provided snapshots of the proteasome during ATP-hydrolysis-driven substrate translocation, and detailed biochemical studies revealed the timing of individual degradation steps, elucidating the mechanisms for substrate selection and the commitment to degradation through conformational transitions. It was uncovered how ubiquitin removal from substrates is mechanically coupled to degradation, and cryo-electron tomography studies gave a glimpse of active proteasomes inside the cell, their subcellular localization, and interactions with protein aggregates. Here, we summarize these advances in our mechanistic understanding of the proteasome, with a particular focus on how its structural features and conformational transitions enable the multi-step degradation process.

Structure and Function of the 26S Proteasome

As the endpoint for the ubiquitin-proteasome system, the 26S proteasome is the principal proteolytic machine responsible for regulated protein degradation in eukaryotic cells. The proteasome's cellular functions range from general protein homeostasis and stress response to the control of vital processes such as cell division and signal transduction. To reliably process all the proteins presented to it in the complex cellular environment, the proteasome must combine high promiscuity with exceptional substrate selectivity. Recent structural and biochemical studies have shed new light on the many steps involved in proteasomal substrate processing, including recognition, deubiquitination, and ATP-driven translocation and unfolding. In addition, these studies revealed a complex conformational landscape that ensures proper substrate selection before the proteasome commits to processive degradation. These advances in our understanding of the proteasome's intricate machinery set the stage for future studies on how the proteasome functions as a major regulator of the eukaryotic proteome.

Molecular-scale features that govern the effects of O-glycosylation on a carbohydrate-binding module

Protein glycosylation is a ubiquitous post-translational modification in all kingdoms of life. Despite its importance in molecular and cellular biology, the molecular-level ramifications of O-glycosylation on biomolecular structure and function remain elusive. Here, we took a small model glycoprotein and changed the glycan structure and size, amino acid residues near the glycosylation site, and glycosidic linkage while monitoring any corresponding changes to physical stability and cellulose binding affinity. The results of this study reveal the collective importance of all the studied features in controlling the most pronounced effects of O-glycosylation in this system. Going forward, this study suggests the possibility of designing proteins with multiple improved properties by simultaneously varying the structures of O-glycans and amino acids local to the glycosylation site.

Glycosylation of Cellulases: Engineering Better Enzymes for Biofuels

Cellulose in plant cell walls is the largest reservoir of renewable carbon on Earth. The saccharification of cellulose from plant biomass into soluble sugars can be achieved using fungal and bacterial cellulolytic enzymes, cellulases, and further converted into fuels and chemicals. Most fungal cellulases are both N- and O-glycosylated in their native form, yet the consequences of glycosylation on activity and structure are not fully understood. Studying protein glycosylation is challenging as glycans are extremely heterogeneous, stereochemically complex, and glycosylation is not under direct genetic control. Despite these limitations, many studies have begun to unveil the role of cellulase glycosylation, especially in the industrially relevant cellobiohydrolase from Trichoderma reesei, Cel7A. Glycosylation confers many beneficial properties to cellulases including enhanced activity, thermal and proteolytic stability, and structural stabilization. However, glycosylation must be controlled carefully as such positive effects can be dampened or reversed. Encouragingly, methods for the manipulation of glycan structures have been recently reported that employ genetic tuning of glycan-active enzymes expressed from homogeneous and heterologous fungal hosts. Taken together, these studies have enabled new strategies for the exploitation of protein glycosylation for the production of enhanced cellulases for biofuel production.

Middle cerebral artery blood flows by combining TCD velocities and MRA diameters: in vitro and in vivo validations

Non-invasive transcranial Doppler (TCD) is widely used for blood velocity (BV, cm/sec) measurements in the human middle cerebral artery (MCA). MCABV measurements are accepted as linear with MCA blood flow (MCABF). Magnetic resonance angiography (MRA) provides measurements of MCA lumen diameters that can be combined with TCD MCABV to calculate MCABF (mL/min). We tested the precision and accuracy of this method against a flow phantom and in vivo proximal internal carotid artery blood flow (ICABF). In vitro precision (repeated measures) and accuracy (vs. time collection) gave correlations coefficients of 0.97 and 0.98, respectively (both p < 0.05). In vivo precision (repeated measures) and accuracy (vs. ICABF) gave correlation coefficients of 0.90 (left and right), 0.94 (left) and 0.93 (right) (all p < 0.05). Bilateral MCABF in 35 adults were similar (left, 168 ± 72 mL/min; right, 180 ± 69 mL/min; p > 0.05). Results suggest that blood velocity by TCD and lumen diameter by MRA can be combined to estimate absolute values of MCABF.

Middle cerebral artery resistivity and pulsatility indices in systemic lupus erythematosus: evidence for hyperperfusion

BACKGROUND AND PURPOSE

Systemic lupus erythematosus (SLE) is associated with significant cerebrovascular and neuropsychiatric disease for which multiple pathogeneses have been proposed. Although global cerebral hypoperfusion has been proposed, there are limited data about intracerebral arterial hemodynamics. Transcranial Doppler (TCD) allows portable, high temporal and spatial resolution, noninvasive blood velocity measurements in the middle cerebral arteries, and calculations of standard resistivity (RI) and pulsatility (PI) indices. RI and PI correlate with cerebral hemispheric arteriolar tone, blood flow resistances, and impedances. Accordingly, we hypothesized that there would be significant differences (p < 0.05) in RI and PI between SLE patients and healthy, age and gender matched controls.

METHODS

TCD was used to measure RI and PI bilaterally on 34 stable SLE patients (35 ± 11 years) and 15 control subjects (34 ± 10 years). Patients and controls had similar, normal blood pressures and were examined in the supine position during normal, resting respiration. RI and PI were determined by a blinded, experienced observer.

RESULTS

There were no significant differences in RI and PI bilaterally within each cohort. However, SLE patients had significantly lower average RI and PI values compared with controls: 0.45 ± 0.10 versus 0.52 ± 0.05 (p < 0.05); and 0.65 ± 0.19 versus 0.77 ± 0.12, (p < 0.05); respectively.

CONCLUSIONS

These preliminary data suggest that RI and PI values in the human middle cerebral artery are significantly lower in SLE compared with controls. These indices indicate that middle cerebral arterial resistances and impedances are decreased in SLE. Under normotensive conditions, the results are consistent with hyperperfusion in SLE with increased arteriolar dilation and increased cerebral blood flow.

Noninvasive transthoracic and transesophageal Doppler echocardiographic measurements of human coronary blood flow velocity: In vitro flow phantom validation

Coronary angiography is limited in assessing the hemodynamic significance of a coronary lesion or the state of the coronary microcirculation. Noninvasive transthoracic (TTE) and transesophageal (TEE) Doppler echocardiography have been used to measure coronary blood flow velocity and coronary flow reserve and thus the physiology of the coronary vasculature (normal, stable or unstable lesions). A fundamental, in vitro validation of these methods with a tissue and blood mimicking flow phantom has not been reported. Accordingly, Bland-Altman 95% confidence levels for precision (repeated measures) and accuracy (comparison with time collection) were determined for both TTE and TEE measurements of simulated coronary diastolic blood velocities in 2 mm and 4 mm vessels at the normal in vivo depths of 40 mm and 60 mm. The Doppler angle was set at 45 degrees and flow velocities were varied within a normal in vivo range of 0- 150 cm/s. Confidence levels for precisions and accuracies were similar between TTE and TEE and ranged from ± 6 cm/s to ± 13 cm/s or approximately 10-15% over the range of the measured velocities. These in vitro results in a controlled flow phantom suggest that technically adequate TTE and TEE can be used to reliably measure epicardial coronary conduit artery blood flow velocities.

Arterial distensibility in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a prototypical autoimmune disease that is atherogenic. Decreased arterial distensibility (AD) is a risk factor for cardiovascular disease, and this precursor may be associated with SLE. Accordingly, we tested the hypothesis that patients with SLE will have significantly (p < 0.05) decreased AD when compared to normal, healthy age, and gender matched controls. Noninvasive, high resolution ultrasound was performed on 30 patients with chronic SLE and 16 age and gender matched controls. All were female. Maximum systolic and minimum diastolic diameters (mm) and intima-media thickness (IMT, mm) in the right common carotid artery were measured from M-mode images. In vitro arterial models were used for quality control. With a single, blinded observer, the 95% confidence levels for accuracy and precision for noninvasive systolic and diastolic tonometric arm blood pressures (SBP, DBP) and carotid sonographic diameters were approximately 5 mmHg and approximately 0.10 mm, respectively. Derived measurements for strain (%), stiffness (units), and AD (units) were determined by published arterial mechanical models and algorithms. Results (mean/standard deviation) were as follows: (patients/controls; # =p<0.05) Age 39/11, 35/11 years; SBP 130/20, 117/8# mmHg; DBP 82/11, 74/9# mmHg; strain 11/4, 11/4 %); stiffness 19/10, 17/11 units; IMT 0.44/0.08, 0.41/0.06 mm; AD 3.10/1.49, 3.30/1.63 units. There were no statistically significant differences (p<0.05) in measurements of AD and IMT in the common carotid artery between relatively young SLE patients and well matched controls.

Doppler ultrasound determination of the distribution of human cardiac output: effects of age and physical stresses

Due to its high spatial, temporal, and dynamic resolution, noninvasive Doppler ultrasound can be used to determine the distribution of phasic cardiac output in humans. The effects of ageing and various common physical stresses on combined human major central and regional blood flows have not been reported. We tested the hypothesis that there are no significant age-related differences in steady-state human central and regional hemodynamics during leg exercise, hypoxia, eating, and standing. We used noninvasive, image-guided Doppler flowmetry (approximately 7% linearity, approximately 11% accuracy) to measure absolute values and percent changes (%C) in phasic blood flows in the following major arteries: ascending aorta (CO, cardiac output), common carotid (CQ, brain), subclavian (SQ, arm), renal (RQ, kidney), superior mesenteric (MQ, gut), and common femoral (FQ, leg). Mean arm cuff blood pressure (BP), heart rate (HR), stroke volume (SV), and total peripheral resistance (PR) were also determined. We studied 16 young (Y, 24/3 years, 8 males) and 16 elderly (E, 73/2 years, 7 males) healthy, lean adults during separate experiments of: 50% submaximal leg exercise; 12% oxygen breathing; ~700 calorie meal; and 70 degrees upright tilt. Exercise results (X/SD) are given as Y(%C) then E(%C) where (+) represents p<0.05 vs resting, fasting control: HR: 78/8+,66/7+; BP: 6/5,8/6; SV: - 15/5+,21/4+; CO: 96/11+,87/9+; PR: -83/13+,- 76/10+; CQ: 16/8+,14/6+; SQ: -6/8,-12/8; MQ: -21/11+,-15/11; RQ: -14/8/-12/7; FQ: 919/88+,898/74 Importantly, there were no significant (p<0.05) age-related differences in the percentage changes in any of these hemodynamic variables. Similar results were found during hypoxia, eating, and standing. We conclude that although physical stresses significantly (p<0.05) affects various central and regional hemodynamics, there are no significant age-related differences in these variables between healthy, successfully aged, 20 and 70 year old cohorts. These data suggest that given an appropriate genetic template and behavior free of significant trauma and disease states, cardiovascular control mechanisms and the distributions of cardiac output during common, daily, physical stresses are maintained with age through 70 years of life.

Cardiac output measurements in congenital heart disease: validation of a simple, portable Doppler method

Noninvasive Doppler cardiac output measurements are clinical standards in adults and children. Presently, these standard Doppler methods generally require relatively expensive and large imaging equipment with complex signal-processing techniques. Thus, universal access to these important measurements has been limited. Simple, portable Doppler methods have been validated previously and applied to infants and children without cardiac disease. Nevertheless, these specific, inexpensive techniques have not been validated in children with complex congenital heart disease. Accordingly, we compared a noninvasive, suprasternal, non-image-guided, pulsed Doppler cardiac output with standard invasive Fick cardiac outputs in 20 patients (age range, 1 month to 15 years) with congenital heart disease. Doppler cardiac output was displayed by multiplying the mean velocity with an operator-selected angiographic or echographic estimate of the aortic diameter. The values from linear regression analysis were r = 0.96; Doppler cardiac output = 0.98 x Fick cardiac output - 0.08 L/min (range, 0.55-3.10 L/min). The 95% confidence limits were less than 35% of the mean of Doppler and Fick cardiac outputs across the range of measurements. We conclude that relatively linear and accurate measurements of cardiac output can be made by this simple, inexpensive, portable method in selected infants and children with various forms of congenital heart disease.

Human middle cerebral artery blood velocity during sexual intercourse

Although the augmentation of central hemodynamics during human sexual intercourse is well established, dynamic changes in human regional cerebral blood flow have not been reported. Noninvasive transcranial Doppler ultrasonography has been well validated and allows direct, continuous measurement of phasic blood velocity in the human middle cerebral artery (a linear index of regional cerebral blood flow). The middle cerebral artery supplies the premotor and primary sensorimotor cortical regions for the arms, upper and lower trunk, and head. Blood velocities in this vessel have been shown to increase significantly with sensory stimuli and physical stresses. Accordingly, we tested the hypothesis that human sexual intercourse increases middle cerebral artery blood velocity. We used noninvasive, transcranial Doppler ultrasonography (95% confidence limits for precision +/- 7%) to measure blood velocity in the left middle cerebral artery of 10 male and 10 female, sexually acquainted, healthy adults (age range, 23 to 47 years; mean, 30 years). To eliminate signal artifacts and allow complete freedom of motion, a modified low profile, temporal fossa transducer was secured by minimal unobtrusive forehead strapping. Continuous measurements of phasic blood velocity and heart rate were made in a private bedroom setting during rest (control), preexcitement, excitation, prepenetration, penetration, preorgasm, orgasm, and resolution with the untethered instrumented subject in the supine missionary position. Heart rate and blood velocity responses were similar in both sexes. During orgasm, the maximal heart rate increased significantly (P < 0.05): 49 +/- 44% in women, 65 +/- 32% in men, and 58 +/- 38% combined from a combined resting value of 77 +/- 11 standard deviations SD beats per minute. Importantly, blood velocity in the middle cerebral artery of the 20 subjects remained unchanged (P > 0.10) from a resting value of 56 +/- 15 cm/s. In conclusion, in both sexes, human middle cerebral artery blood velocity, a linear index of human regional cerebral blood flow, does not increase significantly (P > 0.10) during human sexual intercourse.

Arterial oxygen saturation for prediction of acute mountain sickness

BACKGROUND

Acute mountain sickness (AMS) is a usually self-limiting syndrome encompassing headache, nausea and dizziness. AMS is seen in those that go from low to high altitudes too quickly, without allowing sufficient time to acclimatize. At present, susceptibility to AMS cannot be predicted. One feature of AMS noted in some studies is impaired gas exchange. If impaired gas exchange presages AMS then those individuals with exaggerated hypoxemia at high altitude may be more likely to develop AMS. If true, then monitoring of arterial oxygen saturation (SaO2%) may differentiate AMS-resistant individuals from those with impending AMS.

METHODS

To test this hypothesis, we measured SaO2% and AMS symptom scores in 102 healthy asymptomatic climbers at 4200 m on Denali (Mt. McKinley) prior to their further ascent toward the summit at 6194 m, and on their return from higher altitudes to 4200 m.

RESULTS

The results show that exaggerated hypoxemia in asymptomatic climbers prior to further ascent correlates with subsequent AMS (r = -0.48, p < 0.001). Criteria are presented for identification of 80-100% of those climbers who later become ill with AMS.

CONCLUSION

We conclude that resting arterial hypoxemia is related to later development of clinical AMS, and can exclude the occurrence and caution those at risk for development of subsequent AMS. Likely mechanisms are hypoventilation relative to normally acclimatizing individuals and/or abnormalities of gas exchange. Thus, non-invasive oximetry provides a simple, specific indicator of inadequate acclimatization to high altitudes and impending AMS.

Temporal inhomogeneity in brachial artery blood flow during forearm exercise

The purpose of this study was to measure the influences of muscle contraction and exercise intensity on brachial artery blood flow during incremental forearm wrist flexion exercise to fatigue. Twelve subjects performed incremental forearm exercise (increments of 0.1 W every 5 min) with their nondominant arms. Doppler waveforms and two-dimensional images of the brachial artery were recorded during the last 2 min of each stage. Exercise intensities were expressed as a percent of the maximal workload achieved (%WLmax). Blood flow was calculated during each of the concentric (CP), eccentric (EP), and recovery phases (RP) of the contraction cycle. Blood flow during the CP of the contraction did not increase above resting values (25.0 +/- 10.5 mL.min-1) at any intensity (100%WLmax = 21.6 +/- 6.5 mL.min-1). Conversely, blood flow during the EP and RP increased from 25.6 +/- 3.0 to 169.1 +/- 12.8 (P < 0.05), and from 24.7 +/- 3.1 to 137.9 +/- 19.5 mL.min-1 (P < 0.05), respectively from rest to maximal exercise. Time averaged blood flow increased linearly from rest to maximal exercise (75.3 +/- 26.3 to 334.6 +/- 141.6 mL.min-1, P < 0.05). Thus, a significant impairment in blood flow occurs with concentric contractions during forearm dynamic exercise. The implications of a temporal disparity in blood flow to oxygen delivery and skeletal metabolism during exercise are discussed.

Central vascular flow patterns in the alligator Alligator mississipiensis

Many different flow patterns have been described through the central circulation of crocodilian reptiles. We tested the hypothesis that the vagus nerve stimulation promotes right-to-left (R-L) shunting in the alligator. Flow patterns were investigated before and during stimulation of the intact left vagus nerve using three methods. 1) Atrial and aortic PO2 were measured simultaneously and continuously by gas probes. 2) Atrial outflows were tracked with a blood tracer (helium). 3) Flows were assessed with echocardiography. Four different flow patterns were observed before vagal stimulation: left ventricular (LV) blood flowed into both the right (RAo) and left (LAo) aortas, whereas right ventricular (RV) blood flowed only into the LAo; both aortas received a mixture of LV and RV blood; only LV blood perfused both aortas; and RV blood flowed into both aortas, but LV blood flowed only into the RAo. During vagal stimulation, both aortas received a mixture of LV and RV blood in half of the animals, and in the other half, both aortas received RV blood, but LV blood flowed only into the RAo. Doppler and contrast echocardiography demonstrated swirling flow in the foramen of Panizza and the base of the LAo during systole. These data indicate that vagal stimulation either maintains or produces R-L shunting, flow patterns are variable, and blood can swirl in the foramen of Panizza and LAo base.

Hemodynamic effects of nasal and face mask continuous positive airway pressure

Studies of the hemodynamic effects of nasal continuous positive airway pressure (n-CPAP) in normal subjects have had conflicting results. The largest study (n = 19) found no effect of up to 15 cm H2O on heart rate (HR), cardiac stroke volume (SV), or cardiac index. We hypothesized that n-CPAP, by increasing intrathoracic pressure, should decrease SV and cardiac output (CO) in a dose-dependent fashion in normal subjects. We also hypothesized that mouth position, i.e., open or closed, could affect intrathoracic pressure and thus SV and CO. Six normal subjects were tested with four levels of CPAP (5, 10, 15, and 20 cm H2O) under three mask conditions-face mask and nasal mask with the mouth open (mo) or with the mouth closed (mc). Noninvasive pulsed Doppler measurements of SV and HR were made under each condition. N-CPAP (mc) and face mask CPAP (f-CPAP) resulted in significant dose-dependent decreases of SV-24 +/- 5 ml (21%) and 33 +/- 5 ml (28%), respectively--from baseline to 20 cm H2O (p < 0.05). HR were unchanged and CO significantly decreased with n-CPAP(mc) and with f-CPAP, 1.6 +/- 0.38 L/min (23%) and 2.29 +/- 0.54 L/min (31%), respectively, from baseline to 20 cm H2O (p < 0.05). Esophageal pressure measurements verified increasing intrathoracic pressure with increasing levels of f-CPAP and n-CPAP (mc) but not with n-CPAP (mo). In conclusion, n-CPAP (mc) and f-CPAP resulted in significant and similar dose-dependent decreases in SV and CO.

Hemodynamic comparison of microsurgical repairs for large arterial defects

Twenty-eight femoral arteries in 14 rats were used to compare transverse closures and end-to-end anastomoses in blood vessels approximately 1 mm in diameter. The transverse closures were applied to arteriectomies created by excising one-half the circumference of the vessel over a length of 1 mm. The end-to-end anastomoses were performed after resecting a 1-mm segment. Recordings were made of pre- and postrepair flow velocity and three-point diameter measurements every 5 minutes using a 20-MHz pulsed Doppler velocimeter and digimatic caliper. Maximum reductions in flow velocity were 18% and 31% for the transverse repair and end-to-end anastomosis, respectively. Otherwise, intergroup comparisons of the postrepair normalization of both flow velocity and vessel diameter showed few significant differences (P < 0.05). We conclude that arterial defects involving no more than half the diameter of the vessel can be effectively repaired in significantly less time using the transverse closure.

Effects of prolonged head-down bed rest on physiological responses to moderate hypoxia

To determine the effects of hypoxia on physiological responses to simulated zero-gravity, cardiopulmonary and fluid balance measurements were made in 6 subjects (acclimatized to 5,400 ft) before and during 5 degrees head-down bed rest (HDBR) over 8 d at 10,678 ft and a second time at this altitude as controls (CON). The VO2max increased by 9% after CON, but fell 3% after HDBR (p < 0.05). This reduction in work capacity during HDBR could be accounted for by inactivity. The heart rate response to a head-up tilt was greatly enhanced following HDBR, while mean blood pressure was lower. No significant negative impact of HDBR was noted on the ability to acclimatize to hypoxia in terms of pulmonary mechanics, gas exchange, circulatory or mental function measurements. No evidence of pulmonary interstitial edema or congestion was noted during HDBR at the lower PIO2 and blood rheology properties were not negatively altered. Symptoms of altitude illness were more prevalent, but not marked, during HDBR and arterial blood gases and oxygenation were not seriously effected by simulated microgravity. Declines in base excess with altitude were similar in both conditions. The study demonstrated a minimal effect of HDBR on the ability to adjust to this level of hypoxia.

Hemodynamic comparison of microsurgical closures for longitudinal arteriotomies

Twenty-four femoral arteries in 12 rats were used to compare longitudinal and transverse closures in blood vessels approximately 1 mm in diameter. The closure techniques were applied to a simple longitudinal slit, 1 mm long, and to a longitudinal defect, 0.5 mm wide and 1 mm long. Comparisons were made of the change in pre- and postrepair flow velocities, recorded every 5 min using a 20-MHz pulsed Doppler velocimeter. Maximum reductions in flow velocity (linearly related to volume flow) were 10% and 29% for the longitudinal and transverse repairs, respectively, when applied to the longitudinal slit, and 65% and 19%, respectively, when applied to the larger arteriotomy. An analysis of variance indicates that the differences in the normalization of flow velocities during the immediate postrepair period are significant (P < 0.05). We conclude that optimal flow normalization is achieved by applying the longitudinal repair to the simple slit and the transverse repair to the larger arteriotomy.

The effect of vasodilators on pulmonary hemodynamics in high altitude pulmonary edema: a comparison

High altitude pulmonary edema is characterized hemodynamically by a markedly restricted pulmonary vascular bed. Pulmonary vascular resistance is six to eight times higher than control values at altitude, and mean pulmonary pressure is generally elevated two to four-fold over control values. We wished to compare the effect of various vasodilators on the hemodynamics of HAPE, both to gauge their potential effectiveness in treatment of HAPE, and also to gain clues as to the mechanism of the altered pulmonary circulation. In a series of field experiments using a total of 16 subjects with HAPE and 10 well controls, we measured pulmonary hemodynamics by non-invasive Doppler echocardiography. The per cent reduction in pulmonary vascular resistance and mean pulmonary artery pressure, respectively, were 46 and 33 for oxygen, 30 and 29 for nifedipine, 29 and 25 with hydralazine, 57 and 42 with phentolamine, and 72 and 52 when oxygen and phentolamine were combined. All the vasodilators improved gas exchange, suggesting a link between edema formation and pulmonary vasoconstriction. A number of vasodilators may be useful in the treatment of HAPE; the superiority of an alpha adrenergic blocker may implicate the sympathetic nervous system in the pathophysiology of high altitude pulmonary edema.

Internal carotid flow velocity with exercise before and after acclimatization to 4,300 m

Cerebral blood flow and O2 delivery during exercise are important for well-being at altitude but have not been studied. We expected flow to increase on arrival at altitude and then to fall as O2 saturation and hemoglobin increased, thereby maintaining cerebral O2 delivery. We used Doppler ultrasound to measure internal carotid artery flow velocity at sea level and on Pikes Peak, CO (4,300 m). In an initial study (1987, n = 7 men) done to determine the effect of brief (5-min) exercises of increasing intensity, we found at sea level that velocity [24.8 +/- 1.4 (SE) cm/s rest] increased by 15 +/- 7, 30 +/- 6, and 22 +/- 8% for cycle exercises at 33, 71, and 96% of maximal O2 uptake, respectively. During acute hypobaric hypoxia in a decompression chamber (inspired PO2 = 83 Torr), velocity (23.2 +/- 1.4 cm/s rest) increased by 33 +/- 6, 20 +/- 5, and 17 +/- 9% for exercises at 45, 72, and 98% of maximal O2 uptake, respectively. After 18 days on Pikes Peak (inspired PO2 = 87 Torr), velocity (26.6 +/- 1.5 cm/s rest) did not increase with exercise. A subsequent study (1988, n = 7 men) of the effect of prolonged exercise (45 min at approximately 100 W) found at sea level that velocity (24.8 +/- 1.7 cm/s rest) increased by 22 +/- 6, 13 +/- 5, 17 +/- 4, and 12 +/- 3% at 5, 15, 30, and 45 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Left ventricular hemodynamics during exercise recovery

The directional response of human left ventricular stroke volume during exercise recovery is unclear. Stroke volume has been reported to increase and decrease over exercise values during early recovery. The confounding variable may be posture. With the use of pulsed Doppler ultrasound, we tested the hypothesis that there is a significant difference between seated and supine stroke index (SI) during passive recovery from seated ergometer exercise. Thirteen subjects aged 26 +/- 2 yr performed two seated cycle ergometer exercise tests to 70% of predicted maximum heart rate (HR). Recovery was supine on one test and seated on the other. Cardiac index (CI), HR, and SI were calculated during rest, exercise, and 10 min of recovery. At rest, SI and CI were significantly (P less than 0.01) less and HR significantly (P less than 0.01) greater when the subjects were seated than when they were supine. At the last exercise work load, no significant differences were found in any measured variable between tests. During recovery, supine SI was maximal 180 s postexercise (99 +/- 14 ml/m2) and exceeded (P less than 0.01) resting supine (81 +/- 14 ml/m2) and peak exercise (77 +/- 14 ml/m2) SI by 22 and 29%, respectively. Seated SI was constant at peak exercise levels for 2 min. Seated and supine recovery CI never exceeded exercise values. Systolic and diastolic blood pressure recovery curves were similar in the two postures. We conclude that posture significantly affects SI during recovery from submaximal seated exercise. These results have implications for choice of recovery posture after stress testing in cardiac patients where it is desirable to minimize ventricular loading.

Effects of exercise training on common femoral artery blood flow in patients with intermittent claudication

Exercise training is a commonly used rehabilitative therapy for patients with intermittent claudication (IC). However, it is not known whether blood flow through the major conduit vessel of the leg, the common femoral artery (CFA), increases with exercise training. We tested the hypothesis that peak CFA blood flow will increase with a supervised, lengthy, and individualized exercise training program. Subjects were 10 IC patients (eight men, two women) with a mean age of 61 +/- 7 (mean +/- SD) years who had either aortoiliac (n = 7) or femoropopliteal (n = 3) stenosis. Using noninvasive Doppler flowmetry, we measured CFA blood flow and ankle pressure at rest and after a maximum symptom-limited graded treadmill test before (T1) and after 3 (T2) and 5 (T3) months of exercise training. Variables were measured in the supine and upright postures at rest and during recovery. Total walking distance and claudication distance on the treadmill were determined for T1, T2, and T3. After training, CFA blood flow and ankle pressure were not significantly higher at rest or at 1 minute after exercise compared with pretraining despite significant increases in claudication and total walking distances. The rate of CFA blood flow recovery was slower at T3, suggesting the accrual of a larger metabolic debt during exercise due to more work performed. We conclude that changes in CFA blood flow are not responsible for measured changes in performance with exercise training in IC patients.

Effect of a high-protein meal on blood flow to transplanted human kidneys

Renal blood flow in normal adults increases after protein ingestion. The mechanisms that create this hyperperfusion are unclear. A neurogenic factor in humans has not been definitively ruled out. Accordingly, we tested the hypothesis that a high-protein meal significantly increases renal blood flow to the denervated human kidney. We studied 11 transplant recipients (TR) with denervated kidneys and 4 kidney donors (KD) with a single innervated kidney. All subjects had normal urinalysis. Using noninvasive Doppler flowmetry that was previously validated, we determined renal blood flow (RQ, ml/min) after a 12-hr fast (F) and 1, 2, and 3 hr after a high-protein meal (500 ml) of 150 g protein, 30 g fat, and 30 g carbohydrate. The RQ (mean +/- SD, ml/min) at fasting and at 1, 2, and 3 hr postprandially was 409 +/- 100, 446 +/- 100, 493 +/- 122 (P less than 0.05 vs. F), and 500 +/- 123 (P less than 0.05 vs. F), respectively, for the TR, and was 654 +/- 60 (P less than 0.05 vs. TR), 667 +/- 86 (P less than 0.05 vs. TR), 776 +/- 80 (P less than 0.05 vs. F and TR), and 809 +/- 81 (P less than 0.05 vs. F and TR) for KD. We conclude that RQ in TR increases significantly after protein ingestion. Thus, in the noninstrumented, unanesthetized human with a transplanted kidney, neural control is not a factor in the increase in renal blood flow after a high protein meal.

Clinical evaluation versus Doppler echocardiography in the quantitative assessment of valvular heart disease

We tested the hypotheses that Doppler echocardiography has a higher accuracy than clinical evaluation in the detection of significant aortic and mitral valvular heart disease and that Doppler echocardiography is highly accurate as compared with cardiac catheterization for the assessment of valvular disease severity. Thus, cardiac catheterization for the assessment of valve lesion severity may be unnecessary in selected patients. We prospectively evaluated 75 consecutive patients, ages 20-74 years (mean, 52 years), with clinically suspected valvular heart disease. Specific clinical and Doppler echocardiographic criteria were used to categorize each valve lesion as absent, insignificant, or significant. Criteria for a significant lesion at cardiac catheterization was an aortic or mitral valve area less than 1.1 or 1.5 cm2, respectively, or equal to or greater than 3+ cm2 aortic or mitral regurgitation at angiography. In all valve lesions, Doppler echocardiography had a higher overall accuracy than clinical evaluation. Increases in accuracies of 28%, 19%, 15%, and 7% occurred for mitral stenosis, aortic stenosis, aortic regurgitation, and mitral regurgitation, respectively, resulting in overall accuracies of 97%, 100%, 95%, and 96%. Clinical evaluation alone made 28 errors (37% of patients and 19% of valve lesions assessed), and 17 of these errors (23% of patients and 12% of valve lesions) would have resulted in inappropriate management. In only four (24%) of these 17 patients, the attending cardiologist would not have proceeded to assess the valve at cardiac catheterization.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulsed ultrasound Doppler velocimetry in the assessment of microvascular hemodynamics

Pulsed ultrasonic Doppler velocimetry (20 MHz) (PUDVM) has evolved considerably in the last 10 years. Engineering development has resulted in a computer-controlled vessel-scanning instrument whose backscattered frequency shift spectra are analyzed using fast Fourier transforms (FFT). Benchtop and theoretic studies indicate accurate (error less than 5%) velocity and volumetric flow rate measurements in vessels with a lumen diameter as small as 1.2 mm. Clinical application of the PUDVM has provided transcutaneous measurements of blood flow variables in normal human digital arteries. Experimental application to arteries 1.0-1.5 mm has provided information on the hemodynamic effects of topical vasodilators, standard microarteriorrhaphy, variations in microvascular technique, interpositional grafts, and early wound repair. With improving computer capabilities and technical modifications, the PUDVM will be an increasingly important tool in clinical and experimental microsurgery.

Doppler predictions of pulmonary artery pressure, flow, and resistance in adults

We examined the accuracy of noninvasive predictions of pulmonary artery pressure (P), flow (Q), and resistance (R) by means of main pulmonary artery blood velocities and diameters measured with Doppler echocardiography (DE). The ratio of noninvasive acceleration time to ejection time (An) was correlated to invasively determined mean pulmonary artery pressure (Pl) and resistance (Rl). Noninvasive flows were correlated to thermodilution flows (Ql). Simultaneous invasive and noninvasive measurements were made in nine adult patients (ages = 22 to 73 years). The results were: Pl = 87 - 152An, r = 0.90, SEE = 7 mm Hg, p less than 0.05; Rl = 899 - 1722An, r = 0.79, SEE = 121 dynes X sec X cm-5, p less than 0.05; and Ql = -0.3 + 1.21Qn, r = 0.95, SEE = 0.81 L X min-1, p less than 0.05. We then used these equations prospectively to predict Pl, Rl, and Ql in 21 of 25 (83% technically adequate) consecutive patients. Pl, Rl, and Ql ranged from 10 to 35 mm Hg, 39 to 456 dynes X sec X cm-5, and 3.51 to 8.39 L X min-1, respectively. Results were: Pl = 0.80P + 3, r = 0.72, SEE = 6 mm Hg, p less than 0.05; Rl = 0.75R - 12, r = 0.64, SEE = 77 dynes X sec X cm-5, p less than 0.005; and Ql = 0.87Q + 0.38, r = 0.83, SEE = 0.86 L X min-1, p less than 0.05. These results suggest that DE predictions of pulmonary artery pressure, flow, and resistance correlate significantly with values subsequently obtained at catheterization.

Noninvasive Doppler assessment of human postprandial renal blood flow and cardiac output

We compared the effects of protein, carbohydrate, or water ingestion on human renal blood flow (RBF) and cardiac output (CO). We validated and applied a noninvasive ultrasonic Doppler method to measure blood velocities and lumen diameters in the right renal artery and the ascending aorta of five healthy adults. From these measurements, we calculated the average RBF and CO over five cardiac cycles. Normalizing to body surface area, renal blood flow index to one kidney (RI) and cardiac index (CI) were calculated. The percentage of the CI distributed to a single kidney was determined as %CI = RI/CI. Subjects were studied randomly on three separate days after ingestion of each of the following equivolume (500 ml) meals: 1) 150 g protein, 30 g fat, and 30 g carbohydrate (P); 2) 150 g carbohydrate, 30 g fat, and 30 g protein (C); and 3) water. Data were obtained after 12 h of fasting and at 30, 60, 90, 120, 180, and 240 min postprandially. Analysis of covariance revealed significant (P less than 0.05) increases from fasting levels in postprandial RI at 90 to 240 min after P. Postprandial RI with P was significantly higher than with C at 180 and 240 min. Postprandial %CI with P and C decreased significantly from the fasting value at 30 to 180 min. Heart rate and mean arm cuff blood pressure did not change significantly with any diet. Results suggest that the protein-rich meal evokes a more sustained increase in postprandial RI than the carbohydrate rich meal. Despite the increase in postprandial RI, the percentage of cardiac output perfusing a kidney declines similarly with both diets.

Aortic blood flow during sequential MAST inflation

Cardiac output, pulse rate, blood pressure, and distal abdominal aortic blood flow were measured in ten healthy volunteers during sequential inflation of medical antishock trousers. Full inflation of all three compartments decreased distal aortic blood flow by three quarters (P less than .001) and increased blood pressure by 10% (P less than .001), but had no effect on cardiac output or pulse rate. Inflation to lower pressures was markedly less effective.

Noninvasive Doppler flowmetry for measuring regional blood flow

Ultrasonic Doppler flowmetry should assume an increasingly important role in the serial evaluation of human cardiovascular physiology. The principal advantages of this method are that it (1) is noninvasive, (2) is nontraumatic, (3) provides anatomic and physiologic data, and (4) provides dynamic measurements. Nevertheless, the equally important limitations of the technique are that it (1) is difficult to apply in some subjects (ie, those who are obese or have anatomic variations), (2) requires operator skill and a thorough knowledge of human anatomy and cardiovascular dynamics, (3) has a finite spatial resolution that may compromise the measurement of small (1 mm) vessel diameters, and (4) has a finite velocity-measuring capability that will affect measurements of blood velocities outside the range of approximately 2 to 200 cm/sec. Full appreciation of the capabilities and limitations of noninvasive ultrasonic Doppler flowmetry makes possible a better understanding of the dynamic interplay of anatomy, pressure, flow, and resistance in the normal and abnormal intact human cardiovascular system.

Noninvasive Doppler determination of cardiac output during submaximal and peak exercise

We compared pulsed Doppler (PD) measurements of stroke volume (SV) and cardiac output (CO) as a function of work load with previously reported values that were obtained by standard invasive methods. Suprasternal notch measurements of Doppler-shifted frequency (delta f) were obtained from the ascending aorta and SV calculated with the Doppler equation and an independent measurement of aortic diameter. Motion artifacts were minimized with the aid of a restraining table cycle ergometer. Signal aliasing was accommodated with manual summation of delta f waveforms. A total of 207 determinations were made in 10 sitting subjects exercising to exhaustion. Linear regression analysis of CO vs. work load was significant (P less than 0.001). The correlation coefficient (r = 0.95) and standard error of estimate value (1.21 1/min) were similar to values from the literature. Absolute values of CO and SV underestimated the literature values across all work loads. Technical reproducibility was assessed by comparing with paired t tests the differences between 65 duplicate serial measurements of CO and SV at rest and exercise. No significant differences (P less than 0.001) were found. We concluded that PD-determined SV and CO are reproducible and correlate linearly with work load in a manner consistent with reported invasive techniques. Thus the PD method appears suitable for use during submaximal and peak exercise.

A comparison of echo-Doppler and electromagnetic renal blood flow measurements

The linearity and accuracy of noninvasive ultrasonic method of measuring beat-to-beat renal blood flow was evaluated by correlation with standard electromagnetic flowmetry. Using a combined real-time ultrasonic imager and pulsed Doppler velocimeter known as a duplex scanner (DS), lumen diameter (D) and average blood velocity (V) within the imaged renal artery were recorded. Renal blood flow ( QDS ) was calculated offline using a microprocessor from the equation QDS = (pi x D2 x V)/4. This noninvasive method had previously been validated in vitro using a controlled hydraulic system which modeled steady-state flow (QT) where QDS = 0.98 QT + 7.75, SEE = +/- 13.2, r = +0.98, P less than 0.001. In three anesthetized dogs, simultaneous QDS and electromagnetic flow ( QEMF ) measurements (range 44-484 ml x min-1) were made in the proximal left renal artery. Linear regression analysis gave QDS = 0.43 QEMF + 40.5, r = 0.78, SEE = 33.8 ml x min-1, P less than 0.01; QDS = 1.2 QEMF + 2.9, r = 0.86, SEE = 20.8 ml x min-1, P less than 0.01; QDS = 0.86 QEMF + 0.2, r = 0.93, SEE = 53.4 ml x min-1, P less than 0.01. These results suggest that noninvasive QDS measurements of renal blood flow are linear and reasonably accurate compared with invasive QEMF in dogs. The method may have utility in the noninvasive measurement of beat-to-beat blood flow in human renal arteries.

Noninvasive diagnosis of renal artery stenosis by echo-Doppler velocimetry

We evaluated the diagnostic accuracy of ultrasonic echo-Doppler velocimetry for the noninvasive diagnosis of renal artery stenosis. Renal artery stenosis was diagnosed if one or more of the following four abnormal hemodynamic parameters were found by Doppler velocimetry: (1) peak blood velocity greater than 100 cm . sec-1 in a focal area along the length of a renal artery, (2) absence of blood velocity during diastole, (3) absence of any detectable blood velocity denoting occlusion, or (4) broad-band Doppler frequency spectra due to focal blood velocity disturbances. With these criteria, the presence or absence of renal artery stenosis was blindly evaluated in 26 patients (52 arteries) who underwent standard or digital subtraction angiography. Compared to arteriography (reduction in diameter greater than or equal to 50%), the sensitivity of Doppler method was 89%, while its specificity was 73%. This noninvasive method may be useful in selecting patients for radiographic evaluation of renal artery stenosis and in the long term follow-up of these patients. Furthermore, echo-Doppler velocimetry may have the unique capability of assessing the hemodynamic consequences of renal artery stenosis.

Femoral blood flow in term and premature infants

A specially designed 20-MHz pulsed Doppler velocity meter was used to quantify noninvasively common femoral artery blood flow and blood flow characteristics in 11 normal term and 12 premature infants. Femoral artery mean velocity (vf), blood flow (Q), weight-normalized blood flow (Q/kg) and pulsatility index (PI) were determined for the two groups. Mean values for Q (+/- SD) in the term and preterm infants were 27.3 +/- 10.3 and 23.4 +/- 14.7 (ml X min-1), respectively (P less than 0.1). Mean Q/kg for the premature infants was significantly higher (22.1 +/- 12.8) than that for the term infants (9.1 +/- 4.2), P less than 0.005. This study demonstrates differences between the pulsatile blood flow and velocity characteristics of the femoral arteries of premature and of full-term infants.

Comparison of noninvasive pulsed Doppler and Fick measurements of stroke volume in cardiac patients

We compared simultaneous measurements of stroke volume by direct Fick (SVF) and noninvasive pulsed Doppler (SVD) techniques in 15 resting, supine cardiac patients. Doppler measurements of ascending aorta blood velocity were obtained from the suprasternal notch with a single crystal transducer. The systolic velocity integral of the spatial-average velocity waveform was multiplied by cross-sectional area from the systolic aortic diameter, obtained independently by M-mode echocardiography, to determine absolute values for SVD. The resulting linear regression equation was SVD = -1.14 + 0.95SVF, r = +0.91, p less than 0.0001. The mean SVD and SVF values were 68 and 73 cm3, respectively. These results in consecutive patients serve to validate empirically the pulsed Doppler method at rest. It is a convenient, safe, and painless procedure which appears appropriate for clinical diagnostic screening where serial measurements would be useful. However, this noninvasive technique does require technical experience and an understanding of anatomy and flow waveforms by the operator to obtain valid measurements.

Echo-Doppler angle determination for noninvasive transmitral blood velocity calculations in normal and porcine bioprosthetic mitral valves

Doppler incident angle (DA) determination is a critical factor in the noninvasive attempt to measure transmitral blood velocity (TMBV) and to estimate volumetric flow. The error in TMBV varies with the cosine of DA. Using an echo-Doppler duplex scanner (DS), we studied transmitral flow velocities in 10 normal subjects (Group I) and 10 asymptomatic patients with procine mitral valve (PMV) bioprostheses. A 3-MHz scanhead with three medium focused rotating transducers was positioned at the left ventricular apex, and standard apical four-chamber views of the heart were obtained. The position of the Doppler sample volume (SV) was adjusted within the valve orifice until the maximal power of the Doppler audio spectra reflecting TMBV was recorded by a spectral analyzer. At this location of the SV, images were recorded and protractors were used to estimate DA. DA ranged from 10 to 40 degrees (x = 22.5 degrees +/- 10.8 degrees) in Group I and from 0 to 15 degrees (x = 4.5 degrees +/- 5.0 degrees) in Group II. Mean values of DA in Groups I and II were significantly different (p less than 0.01). We conclude: (1) in normal subjects, DA measured from the apex into the MV varies significantly and thus may compromise the accuracy of TMBV measurements; (2) the truncated funnel shape of the stent of the PMV bioprosthesis allows a DA less than 15 degrees and thus a smaller error in TMBV calculations.