Respirator tubes were removed from the throat of Barney B. Clark, in his second day with an artificial heart beating in his chest, and he spoke this afternoon for the first time since his surgery.

"He wanted a glass of water and that's not a bad request," said Dr. Chase Peterson, University of Utah vice president for health sciences. Peterson said that the first human recipient of a permanent artificial heart continued to make steady progress and appeared remarkably free of medical complications.

He remained in critical condition in a guarded intensive care unit at the medical center here, but was described as doing "extremely well." Clark's vital signs -- blood pressure, pulse, temperature, cardiac output -- neared the normal range, Peterson said. He was "alert" and "moving all his extremities," and looking much healthier than he had before the operation.

"In essence, he's gone from a man who was blue -- that is, under-oxygenated before surgery -- and he's now a pink condition," said Peterson.

Clark was also able to "vigorously shake hands," said Peterson, with Dr. William DeVries, the surgeon who made medical history by implanting the artificial heart.

Hospital officials said that the speed with which Clark was taken off the respirator was within normal limits for an open heart surgery patient, but that Clark appeared to be doing better than many who undergo coronary bypass operations or valve replacement surgery.

The head nurse in charge of the intensive care unit said that Clark initially appeared to be "doing better" than a patient who underwent standard open heart surgery before him Wednesday night, a spokesman said.

The 61-year-old retired Seattle dentist was near death when his deteriorating heart was replaced with a plastic-and-metal substitute in a 7 1/2-hour operation that began late Wednesday night and ended after dawn Thursday.

He is tethered by 6-foot hoses to a bulky, compressed-air power system -- Peterson likens it to a "grocery cart" -- that must be plugged into an electrical outlet. The apparatus, which contains a backup compressed-air power source in case of power failure, weighs 375 pounds and will use about $20 a month in electricity.

While Clark appeared to be adapting well to the new paraphernalia that will be with him for the rest of his life, doctors here remain concerned that complications may still develop.

None have appeared thus far, said Peterson. "There is no evidence of infection," he said, and fluid that had filled Clark's chest before the operation continued to drain out. As expected, Clark, who is 6 feet, 2 inches tall and weighs over 200 pounds, had lost more than 2 pounds since the surgery.

For the moment, his progress is being watched a day at a time. Peterson emphasized that there was "no one moment" when doctors could say that he was likely to make it. "We want him to continue gaining strength, continue healing."

Peterson said that Clark had already passed through two critical phases, the time when the heart was first implanted yesterday morning and when he regained consciousness in the hours after the operation ended. "We were scared to death," he said, about the possibility of brain damage developing from such a difficult and unprecedented operation.

Now, Peterson said, the third phase is the next week or two, as doctors watch to make sure the incision heals properly and try to get Clark out of bed and walking around. DeVries has said that if all goes well, Clark could go home in a few weeks.

Infection, particularly in the lungs or at the site where the artificial heart tubes leave Clark's body, is the greatest concern, and Peterson noted that the usual risks faced by any open heart surgery patient are still a worry. These include the possibility of collapse of the lungs or blood clots from remaining immobile.

What doctors don't have to worry about, as in the case in a human heart transplant, is the possibility of rejection of the donor heart by the body's immune defense system. Heart transplant patients are also given massive doses of drugs to help prevent rejection of the donated human heart. These also lower the body's resistance and make it more vulnerable to infection.

There will always remain, however, the possibility that the artificial heart equipment may malfunction. But so far it appears to be working well as doctors seek to adjust the machinery to Clark's needs.

While there is no way to control the natural heart rate, the artificial heart can be regulated. Peterson said that Clark's pulse had arbitrarily been set at 85. The rate is variable in most people, ranging from 60 to 100. It speeds up when they are excited.

Clark's blood pressure, as reported at a late morning news briefing, was 129 over 64. Normal blood pressure is in the range of 140 over 90, said Peterson. Before the operation, Clark's blood pressure was abnormally low, as his failing heart was unable to pump blood adequately, with an upper reading of only about 85 and lower of 40.

His temperature was 98.2, only a fraction below the normal figure of 98.6.

His cardiac output, or the amount of blood pumped out of the heart, had risen to a normal resting level of about 7 liters per minute, compared to only 1 when the the operation took place, Peterson added.

With the respirator tube removed, he said that Clark remains attached to drainage tubes and is receiving intravenous fluids. His urine is being eliminated through a catheter. He is receiving a drug to help clear his lungs but needs very little medication for pain, Peterson said.

Despite Clark's serious condition, nurse Helen Kee reported that he is charming the staff in the special intensive care unit. They are "absolutely delighted," she said, with his humor.

Water has apparently been on Clark's mind ever since the operation. Thursday, unable to talk with the tube in his throat, he motioned to a nurse and wrote the letters "HO" on her hand. She appeared puzzled, but a technician recognized this as shorthand for water, or H2O.

Hospital spokesman John Dwan, who met Clark for the first time this morning, said he had also been motioning to the tubes overhead, indicating he was anxious to get rid of them.

At the moment the focus here is on Clark's progress, and DeVries is devoting round-the-clock attention to his care. DeVries and Peterson said they had no definite plans to attempt a second mechanical transplant operation and that it might be months before another was tried.

The mechanical heart itself costs about $16,500, but much of the equipment used to operate it is hand-made and must be reconstructed before another mechanical heart is implanted. De-Vries currently has permission from the Food and Drug Administration to conduct seven of the experimental operations. He is the only person in the country who has received this approval.