My father is 91, lives alone but I do all shopping, provide all meals, take him to his doctors. Can I claim any expenses on my income tax?

I don't believe you can unless you declare your father a dependent...then, there are also income limits.
Speak to an elder care attorney or accountant. There are also some excellent publications on the IRS website.

Your Dad would need to pass the IRS Dependency Requirements for you to be able to claim any of his expenses on your tax return. Below is a very detailed description of the IRS Dependency Requirements, but it may provide some guidance for your situation.

IRS Dependency Test
1. Income Test
The hardest dependency hurdle is the amount of income your parent earns. Their gross income (e.g., capital gains, self-employment income and other taxable income) cannot be more than the exemption amount (unless they are disabled); in 2009 this was $3,650. (Here’s where kids get a break. This threshold is waived for a child younger than 19 or one who is 24 or younger and still in school.)
The income barrier represents TAXABLE income; gross income does not apply to NON-taxable income like social security benefits or retirement distributions (see your tax preparer to determine what portion is taxable). But if your parents had disciplined saving habits and invested in stocks, bonds, and saving accounts, income from dividends, interests, and capital gains can quickly add. In many cases these sources are considered taxable income, which means that many adult children cannot claim mom or dad as a dependent if they add up above the $3,650 threshold.

2. Support Test
The second big hurdle is the support test. To be deemed a dependent for tax purposes, you must prove you are responsible for at least half of a your parent’s expenses for housing, utilities, food, clothing, medical costs over and above what Medicare and supplemental insurance provides.. If you share that responsibility with others (i.e., you and your two brothers), you must provide more than 10% of your parent’s total financial support to claim an exemption for your parents (in addition to meeting the other tests). To do so, you must also obtain IRS form 2120 from each sibling/supporter who provided more than 10% of the support and who has agreed not to take the dependency exemption on their own return.
When your parent lives in your home, to reach the 50%-plus threshold you should take into account the fair-market room rental, food, medicine and other support items. But be careful in determining what constitutes support. Uncle Sam may not agree with what you and your parent consider vital. For example, items such as furniture, appliances or even cars can, in some instances, be counted as support. Other times, the IRS says “no.”
When determining if you provide more than half of your parent’s support costs, remember to factor in their Social Security Benefits if they are using it to cover some of their support items. This is were Social Security may not disqualify them from the Income Test, but does disqualify them from the Support Test. So say mom doesn’t have $3,650 in taxable income, but gets $15,000 in Social Security and uses it to pay for some medicine and buy clothes. In that case, your contribution to her support may not come up to half.
The one bit of wiggle room here is that your parent doesn’t have to live with you. When a parent is able to remain in his or her own house, in an assisted-living facility or in a nursing home, costs you pay for parental support at those locations count toward meeting the IRS requirement.

2b. Multiple Sibling Support Test
Sometimes you don’t have to shoulder the load alone. Many adult children get help from siblings in caring for mom and dad.
Not only does this help maintain your day-to-day bank balance, it also spreads out any tax breaks. When none of you solely pays for half of a parent’s support, but each contributes at least 10% toward parental care, take a look at the IRS’s multiple-support declaration. This form helps you account for the tax implications of a shared-care arrangement.
So say Mom is in a nursing home. Her Social Security covers 40% of the facility’s costs, and you and your two brothers split the remainder, each paying 20%. Since more than half of her support comes from her three kids, she can be claimed as a dependent — but by only one of you. That choice is left to you and your two brothers.
After you and your brothers agree that you can claim mom as a dependent this tax year, file Form 2120, Multiple Support Declaration with your tax return. This form indicates that while several siblings contributed to mom’s support, the others waive any tax-exemption claim.
You also need to get signed statements from your brothers acknowledging that they waived their tax claims. You don’t have to send these documents with your 1040, but keep them in your records in case the IRS ever questions your exemption or medical-deduction claims.
And the best news about a multiple support agreement is that it’s not permanent. Meaning you can rotate it around from tax year to tax year. The next year, another sibling takes the tax exemption and the third brother the next year. Also make sure that the year you claim Mom as a dependent, you, not your siblings, pay her medical costs so that you get the full tax-deduction benefit. Any medical payments a sibling makes, while helpful, will do neither of you any tax good.

Misc Test
3. They are your parent, grandparent, aunt, uncle, or other elderly relative by blood or legal adaption.
4. They must be a citizen or legal resident of the U. S., Canada, or Mexico (certain restrictions apply).
5. A married parent cannot file jointly unless the husband and wife have no tax liability when filing separately.

Next Steps:
While these tax breaks softens the financial blow, it’s not going to cover everything that it’s going to cost you to support your aging parents. Tax breaks won’t substitute for good financial planning. It’s one of the hardest things that children have to do because it deals with finances, but you need to sit down with your parents and siblings and make a plan. For years and years these people have taken care of you. Now that is shifting.

Additional aging parent resources: These online resources offer tips and advice for adult children caring for aging parents:
 www.nlm.nih.gov/medlineplus/caregivers.html — The federal government’s compilation of links to services for older individuals and their caregivers.
 http://www.eldercare.gov/ — The federal Eldercare Locator can put caregivers in touch with local senior services.
 www.familycaregiving101.org — Two associations teamed up to help new caregivers learn the ins and outs of their roles.
 www.medicare.gov/nhcompare — Compare nursing home quality data and find state inspection agencies at this federal site.
 www.strengthforcaring.com — Connect and chat with other caregivers at this site, sponsored by Johnson & Johnson.
Tax Resources:
 IRS Publication 501: Exemption Filing
 IRS Publication 503: Dependent Care

Roseanne is correct. Check out IRS Pub. Credit For The Elderly. Always keep Pub 17 handy.